MFC r312296 and r323254, which is new a socket option

MFC r312296 and r323254, which is new a socket option
SO_TS_CLOCK to pick from several different clock sources to
return timestamps when SO_TIMESTAMP is enabled and two
new nanosecond-precision timestamp types. This also fixes
recvmsg32() system call to properly down-convert layout of the
64-bit structures to match what 32-bit app(s) expect.

Bump __FreeBSD_version to indicate presence of a new
functionality.

Differential Revision:	https://reviews.freebsd.org/D9171