Prevent ip_input() from panicing due to unprotected access
to INADDR_HASH. This is direct commit to stable/10 instead of MFC r339808
due to significant differences in code base.

PR: 220078
Differential Revision: https://reviews.freebsd.org/D12457
Tested-by: Cassiano Peixoto and others

MFC r297985:

Do not overwrite the dchg variable.

It does not cause any real issues because the variable is overwritten
only when the packet is forwarded (and the variable is not used anymore).

Obtained from: pfSense
Sponsored by: Rubicon Communications (Netgate)

Revert 295285 which was an MFC of the tryforward work (r290383,295282,295283)

In the IPFW+NAT+divergent MTU case there is a bug in sening ICMP MTU updates.

Approved by: re (marius, gjb)
Sponsored by: Rubicon Communications (Netgate)

MFC: r290383,295282,295283

Replace the fastforward path with tryforward which does not require a
sysctl and will always be on. The former split between default and
fast forwarding is removed by this commit while preserving the ability
to use all network stack features.

Differential Revision: https://reviews.freebsd.org/D4042
Reviewed by: ae, melifaro, olivier, rwatson
Approved by: re (glebius)
Sponsored by: Rubicon Communications (Netgate)

MFC 285325
Correct issue presented in r285051 by properly initializing variable.

Differential Revision: https://reviews.freebsd.org/D3036

MFC r285051
Avoid doing multiple route lookups for the same destination IP during forwarding.

Differential Revision: https://reviews.freebsd.org/D2964

MFC r265942:
Fix checksum computation. Previously it didn't include carry.

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.

Merge r263091: fix mbuf flags clash that lead to failure of operation
of IPSEC and packet filters.

PR: kern/185876
PR: kern/186755

Merge r261582, r261601, r261610, r261613, r261627, r261640, r261641, r261823,
r261825, r261859, r261875, r261883, r261911, r262027, r262028, r262029,
r262030, r262162 from head.

Large flowtable revamp. See commit messages for merged revisions for
details.

Sponsored by: Netflix

MFC 285325
Correct issue presented in r285051 by properly initializing variable.

Differential Revision: https://reviews.freebsd.org/D3036

MFC r285051
Avoid doing multiple route lookups for the same destination IP during forwarding.

Differential Revision: https://reviews.freebsd.org/D2964

MFC r265942:
Fix checksum computation. Previously it didn't include carry.

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.

Merge r263091: fix mbuf flags clash that lead to failure of operation
of IPSEC and packet filters.

PR: kern/185876
PR: kern/186755

Merge r261582, r261601, r261610, r261613, r261627, r261640, r261641, r261823,
r261825, r261859, r261875, r261883, r261911, r262027, r262028, r262029,
r262030, r262162 from head.

Large flowtable revamp. See commit messages for merged revisions for
details.

Sponsored by: Netflix