SUNRPC: Bury "#ifdef IPV6" in svc_create_xprt()

Clean up:  Bruce observed we have more or less common logic in each of
svc_create_xprt()'s callers:  the check to create an IPv6 RPC listener
socket only if CONFIG_IPV6 is set.  I'm about to add another case
that does just the same.

If we move the ifdefs into __svc_xpo_create(), then svc_create_xprt()
call sites can get rid of the "#ifdef" ugliness, and can use the same
logic with or without IPv6 support available in the kernel.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/lockd/svc.c

@@ -243,11 +243,9 @@ static int make_socks(struct svc_serv *serv)
 	if (err < 0)
 		goto out_err;
 
-#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 	err = create_lockd_family(serv, PF_INET6);
 	if (err < 0 && err != -EAFNOSUPPORT)
 		goto out_err;
-#endif	/* CONFIG_IPV6 || CONFIG_IPV6_MODULE */
 
 	warned = 0;
 	return 0;