net: socket: support hardware timestamp conversion to PHC bound

This patch is to support hardware timestamp conversion to
PHC bound. This applies to both RX and TX since their skb
handling (for TX, it's skb clone in error queue) all goes
through __sock_recv_timestamp.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>