MFC r313401

Fix garbage IP addresses in UDP log_in_vain messages

If multiple threads emit a UDP log_in_vain message concurrently,
or indeed call inet_ntoa() for any other reason,
the IP addresses could be garbage due to concurrent usage of a
single string buffer inside inet_ntoa(). Use inet_ntoa_r() with
two stack buffers instead.

Relnotes: yes
Sponsored by: Dell EMC

MFC r272886:

Add context pointer and source address to the UDP tunnel callback

These are needed for the forthcoming vxlan implementation. The context
pointer means we do not have to use a spare pointer field in the inpcb,
and the source address is required to populate vxlan's forwarding table.

MFC r272844:

Add missing UDP multicast receive dtrace probes

MFC r272797:

Check for mbuf copy failure when there are multiple multicast sockets

This partitular case is the only path where the mbuf could be NULL.
udp_append() checked for a NULL mbuf only after invoking the tunneling
callback. Our only in tree tunneling callback - SCTP - assumed a non
NULL mbuf, and it is a bit odd to make the callbacks responsible for
checking this condition.

This also reduces the differences between the IPv4 and IPv6 code.

MFC r272347:
The default for UDPLITE_RECV_CSCOV is zero. RFC 3828 recommend
that this means full checksum coverage for received packets.
If an application is willing to accept packets with partial
coverage, it is expected to use the socket option and provide
the minimum coverage it accepts.

MFC r272326:
UDPLite requires a checksum. Therefore, discard a received packet if
the checksum is 0.

MFC r272323:
If the checksum coverage field in the UDPLITE header is the length
of the complete UDPLITE packet, the packet has full checksum coverage.
So fix the condition.

MFC r272263:

Checksum coverage values larger than 65535 for UDPLite are invalid.
Check for this when the user calls setsockopt using UDPLITE_{SEND,RECV}CSCOV.

MFC r264212,r264213,r264248,r265776,r265811,r265909:

- Add support for UDP-Lite protocol (RFC 3828) to IPv4 and IPv6 stacks.
Tested with vlc and a test suite [1].
[1] http://www.erg.abdn.ac.uk/~gerrit/udp-lite/files/udplite_linux.tar.gz

Reviewed by: jhb, glebius, adrian

- Fix a logic bug which prevented the sending of UDP packet with 0 checksum.

- Disable TX checksum offload for UDP-Lite completely. It wasn't used for
partial checksum coverage, but even for full checksum coverage it doesn't
work.

MFC r272886:

Add context pointer and source address to the UDP tunnel callback

These are needed for the forthcoming vxlan implementation. The context
pointer means we do not have to use a spare pointer field in the inpcb,
and the source address is required to populate vxlan's forwarding table.

MFC r272844:

Add missing UDP multicast receive dtrace probes

MFC r272797:

Check for mbuf copy failure when there are multiple multicast sockets

This partitular case is the only path where the mbuf could be NULL.
udp_append() checked for a NULL mbuf only after invoking the tunneling
callback. Our only in tree tunneling callback - SCTP - assumed a non
NULL mbuf, and it is a bit odd to make the callbacks responsible for
checking this condition.

This also reduces the differences between the IPv4 and IPv6 code.

MFC r272347:
The default for UDPLITE_RECV_CSCOV is zero. RFC 3828 recommend
that this means full checksum coverage for received packets.
If an application is willing to accept packets with partial
coverage, it is expected to use the socket option and provide
the minimum coverage it accepts.

MFC r272326:
UDPLite requires a checksum. Therefore, discard a received packet if
the checksum is 0.

MFC r272323:
If the checksum coverage field in the UDPLITE header is the length
of the complete UDPLITE packet, the packet has full checksum coverage.
So fix the condition.

MFC r272263:

Checksum coverage values larger than 65535 for UDPLite are invalid.
Check for this when the user calls setsockopt using UDPLITE_{SEND,RECV}CSCOV.

MFC r264212,r264213,r264248,r265776,r265811,r265909:

- Add support for UDP-Lite protocol (RFC 3828) to IPv4 and IPv6 stacks.
Tested with vlc and a test suite [1].
[1] http://www.erg.abdn.ac.uk/~gerrit/udp-lite/files/udplite_linux.tar.gz

Reviewed by: jhb, glebius, adrian

- Fix a logic bug which prevented the sending of UDP packet with 0 checksum.

- Disable TX checksum offload for UDP-Lite completely. It wasn't used for
partial checksum coverage, but even for full checksum coverage it doesn't
work.