[SOCK]: Add udp_hash member to struct proto.

Inspired by the commit ab1e0a13 ([SOCK] proto: Add hashinfo member to 
struct proto) from Arnaldo, I made similar thing for UDP/-Lite IPv4 
and -v6 protocols.

The result is not that exciting, but it removes some levels of
indirection in udpxxx_get_port and saves some space in code and text.

The first step is to union existing hashinfo and new udp_hash on the
struct proto and give a name to this union, since future initialization 
of tcpxxx_prot, dccp_vx_protinfo and udpxxx_protinfo will cause gcc 
warning about inability to initialize anonymous member this way.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>