lib: Fix SA warning

The addr value will never be null because of the way we do the
cli, but the SA system doesn't understand this.  Add an assert
to make it happy.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>

lib/nexthop_group.c

@@ -387,6 +387,13 @@ DEFPY(ecmp_nexthops, ecmp_nexthops_cmd,
 	struct nexthop *nh;
 	bool legal;
 
+	/*
+	 * This is impossible to happen as that the cli parser refuses
+	 * to let you get here without an addr, but the SA system
+	 * does not understand this intricacy
+	 */
+	assert(addr);
+
 	legal = nexthop_group_parse_nexthop(&nhop, addr, intf, name);
 
 	if (nhop.type == NEXTHOP_TYPE_IPV6