RDMA/cma: Fix unknown symbol when CONFIG_IPV6 is not enabled

If IPV6 has not been enabled in the underlying kernel, we must avoid
calling IPV6 procedures in rdma_cm.ko.

This requires using "IS_ENABLED(CONFIG_IPV6)" in "if" statements
surrounding any code which calls external IPV6 procedures.

In the instance fixed here, procedure cma_bind_addr() called
ipv6_addr_type() -- which resulted in calling external procedure
__ipv6_addr_type().

Fixes: 6c26a771 ("RDMA/cma: fix IPv6 address resolution")
Cc: <stable@vger.kernel.org> # v4.2+
Cc: Spencer Baugh <sbaugh@catern.com>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Reviewed-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/cma.c

@@ -2811,7 +2811,8 @@ static int cma_bind_addr(struct rdma_cm_id *id, struct sockaddr *src_addr,
 	if (!src_addr || !src_addr->sa_family) {
 		src_addr = (struct sockaddr *) &id->route.addr.src_addr;
 		src_addr->sa_family = dst_addr->sa_family;
-		if (dst_addr->sa_family == AF_INET6) {
+		if (IS_ENABLED(CONFIG_IPV6) &&
+		    dst_addr->sa_family == AF_INET6) {
 			struct sockaddr_in6 *src_addr6 = (struct sockaddr_in6 *) src_addr;
 			struct sockaddr_in6 *dst_addr6 = (struct sockaddr_in6 *) dst_addr;
 			src_addr6->sin6_scope_id = dst_addr6->sin6_scope_id;