SUNRPC: Support PF_INET6 in one_sock_name()

Add an arm to the switch statement in svc_one_sock_name() so it can
construct the name of PF_INET6 sockets properly.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: Aime Le Rouzic <aime.le-rouzic@bull.net>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>