MFC r292782: Replace sys/crypto/sha2/sha2.c with lib/libmd/sha512c.c

cperciva's libmd implementation is 5-30% faster
The same was done for SHA256 previously in r263218

Approved by: secteam

MFC r285877:
Move including netinet/icmp6.h around to avoid a problem when including
netinet/icmp6.h and net/netmap.h. Both use ni_flags...
This allows to build multistack with SCTP support.

MFC r284515:
Add FIB support for SCTP.
This fixes https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=200379

PR: 200379

MFC r271643:
Chunk IDs are 8 bit entities, not 16 bit.
Thanks to Peter Kasting from Google for drawing
my attention to it.

MFC r271665:
The MTU is handled as a 32-bit entity within the SCTP stack.
This was reported by Peter Kasting from Google.

MFC r271670:
Make a type conversion explicit. When compiling this code on
Windows as part of the SCTP userland stack, this fixes a
warning reported by Peter Kasting from Google.

MFC r271672:
Small cleanup which addresses a warning regaring the truncation
of a 64-bit entity to a 32-bit entity. This issue was reported by
Peter Kasting from Google.

MFC r271673:
Use a consistent type for the number of HMAC algorithms.
This fixes a bug which resulted in a warning on the userland
stack, when compiled on Windows.
Thanks to Peter Kasting from Google for reporting the issue and
provinding a potential fix.

MFC r271674:
Add a explict cast to silence a warning when building
the userland stack on Windows.
This issue was reported by Peter Kasting from Google.

Approved by: re (kib)

MFC r270673:
Announce SCTP support in the kern.features sysctl variables.

MFC r270859:
Enable SCTP support. It runs perfectly fine on a Wandboard quad.

MFC r271204 with manual intervention:
Fix the handling of sysctl variables when used with VIMAGE.
While there do some cleanup of the code.

MFC r271209:
Fix a leak of an address, if the address is scheduled for removal
and the stack is torn down.
Thanks to Peter Bostroem and Jiayang Liu from Google for reporting the
issue.

MFC r271219:
Use SYSCTL_PROC instead of SYSCTL_VNET_PROC.
Suggested by: glebius@

MFC r271221:
Use union sctp_sockstore instead of struct sockaddr_storage. This
eliminates some warnings when building in userland.
Thanks to Patrick Laimbock for reporting this issue.
Remove also some unnecessary casts.
There should be no functional change.

MFC r271228:
Address another warnings reported by Patrick Laimbock when compiling
in userspace. While there, improve consistency.

MFC r271230:
Address warnings generated by the clang analyzer.

Approved by: re (kib)

MFC r268537:
Whitespace changes.

Merge r262763, r262767, r262771, r262806 from head:
- Remove rt_metrics_lite and simply put its members into rtentry.
- Use counter(9) for rt_pksent (former rt_rmx.rmx_pksent). This
removes another cache trashing ++ from packet forwarding path.
- Create zini/fini methods for the rtentry UMA zone. Via initialize
mutex and counter in them.
- Fix reporting of rmx_pksent to routing socket.
- Fix netstat(1) to report "Use" both in kvm(3) and sysctl(3) mode.

MFC r284515:
Add FIB support for SCTP.
This fixes https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=200379

PR: 200379

MFC r271643:
Chunk IDs are 8 bit entities, not 16 bit.
Thanks to Peter Kasting from Google for drawing
my attention to it.

MFC r271665:
The MTU is handled as a 32-bit entity within the SCTP stack.
This was reported by Peter Kasting from Google.

MFC r271670:
Make a type conversion explicit. When compiling this code on
Windows as part of the SCTP userland stack, this fixes a
warning reported by Peter Kasting from Google.

MFC r271672:
Small cleanup which addresses a warning regaring the truncation
of a 64-bit entity to a 32-bit entity. This issue was reported by
Peter Kasting from Google.

MFC r271673:
Use a consistent type for the number of HMAC algorithms.
This fixes a bug which resulted in a warning on the userland
stack, when compiled on Windows.
Thanks to Peter Kasting from Google for reporting the issue and
provinding a potential fix.

MFC r271674:
Add a explict cast to silence a warning when building
the userland stack on Windows.
This issue was reported by Peter Kasting from Google.

Approved by: re (kib)

MFC r270673:
Announce SCTP support in the kern.features sysctl variables.

MFC r270859:
Enable SCTP support. It runs perfectly fine on a Wandboard quad.

MFC r271204 with manual intervention:
Fix the handling of sysctl variables when used with VIMAGE.
While there do some cleanup of the code.

MFC r271209:
Fix a leak of an address, if the address is scheduled for removal
and the stack is torn down.
Thanks to Peter Bostroem and Jiayang Liu from Google for reporting the
issue.

MFC r271219:
Use SYSCTL_PROC instead of SYSCTL_VNET_PROC.
Suggested by: glebius@

MFC r271221:
Use union sctp_sockstore instead of struct sockaddr_storage. This
eliminates some warnings when building in userland.
Thanks to Patrick Laimbock for reporting this issue.
Remove also some unnecessary casts.
There should be no functional change.

MFC r271228:
Address another warnings reported by Patrick Laimbock when compiling
in userspace. While there, improve consistency.

MFC r271230:
Address warnings generated by the clang analyzer.

Approved by: re (kib)

MFC r268537:
Whitespace changes.

Merge r262763, r262767, r262771, r262806 from head:
- Remove rt_metrics_lite and simply put its members into rtentry.
- Use counter(9) for rt_pksent (former rt_rmx.rmx_pksent). This
removes another cache trashing ++ from packet forwarding path.
- Create zini/fini methods for the rtentry UMA zone. Via initialize
mutex and counter in them.
- Fix reporting of rmx_pksent to routing socket.
- Fix netstat(1) to report "Use" both in kvm(3) and sysctl(3) mode.