Merge branch 'ipv6-only-sock'

Kuniyuki Iwashima says:

====================
ipv6: Use ipv6_only_sock helper function.

The first patch removes __ipv6_only_sock(), and the second replaces
ipv6only tests with ipv6_only_sock().
====================

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