rpc.mountd: create client_resolve and change client_compose to take a hostent arg

rpc.mountd: create client_resolve and change client_compose to take a hostent arg

This moves the resolution of IP address to hostent into a helper function
and has other functions call it. Having client_compose take a hostent arg
allows us to avoid an extra hostname lookup in the auth_authenticate
codepath as well. Instead of redoing this lookup in client_compose, we can
simply reuse the hostent that was already generated in auth_authenticate.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Signed-off-by: Neil Brown <neilb@suse.de>