rds: Changed IP address internal representation to struct in6_addr

rds: Changed IP address internal representation to struct in6_addr

This patch changed the internal representation of an IP address to use
struct in6_addr.  IPv4 address is stored as an IPv4 mapped address.
All the functions which take an IP address as argument are also
changed to use struct in6_addr.  But RDS socket layer is not modified
such that it still does not accept IPv6 address from an application.
And RDS layer does not accept nor initiate IPv6 connections.

The RDS netfilter header is changed.  User of RDS netfilter will need
to be re-compiled.

Orabug: 25410192

Signed-off-by: Ka-Cheong Poon <ka-cheong.poon@oracle.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>