[NET]: socket family using RCU

Replace the gross custom locking done in socket code for net_family[]
with simple RCU usage. Some reordering necessary to avoid sleep issues
with sock_alloc.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc net/socket.c
Simple merge