uapi: fix linux/rds.h userspace compilation error

On the kernel side, sockaddr_storage is #define'd to
__kernel_sockaddr_storage.  Replacing struct sockaddr_storage with
struct __kernel_sockaddr_storage defined by <linux/socket.h> fixes
the following linux/rds.h userspace compilation error:

/usr/include/linux/rds.h:226:26: error: field 'dest_addr' has incomplete type
  struct sockaddr_storage dest_addr;
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/rds.h

@@ -35,6 +35,7 @@
 #define _LINUX_RDS_H
 
 #include <linux/types.h>
+#include <linux/socket.h>		/* For __kernel_sockaddr_storage. */
 
 #define RDS_IB_ABI_VERSION		0x301
 
@@ -256,7 +257,7 @@ struct rds_get_mr_args {
 };
 
 struct rds_get_mr_for_dest_args {
-	struct sockaddr_storage	dest_addr;
+	struct __kernel_sockaddr_storage dest_addr;
 	struct rds_iovec 	vec;
 	__u64			cookie_addr;
 	__u64			flags;