Merge branch 'expand-txtimestamp-selftest'

Willem de Bruijn says:

====================
expand txtimestamp selftest

Convert the existing txtimestamp test to run as part of kselftest
and return a pass/fail.

Also expand the variations of timestamping tested, including packet
sockets, ipv6 raw and dgram and passing options using cmsg.

These are enough changes to split across a few patches, even if all
changes are only this one test.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>