RDMA/addr: Add support for translating IPv6 addresses

Add support for translating AF_INET6 addresses to the IB address
translation service.  This requires using struct sockaddr_storage
instead of struct sockaddr wherever an IPv6 address might be stored,
and adding cases to handle IPv6 in addition to IPv4 to the various
translation functions.

Signed-off-by: Aleksey Senin <aleksey@alst60.(none)>
Signed-off-by: Roland Dreier <rolandd@cisco.com>