uapi: fix linux/rxrpc.h userspace compilation errors

Consistently use types provided by <linux/types.h> to fix the following
linux/rxrpc.h userspace compilation errors:

/usr/include/linux/rxrpc.h:24:2: error: unknown type name 'u16'
  u16  srx_service; /* service desired */
/usr/include/linux/rxrpc.h:25:2: error: unknown type name 'u16'
  u16  transport_type; /* type of transport socket (SOCK_DGRAM) */
/usr/include/linux/rxrpc.h:26:2: error: unknown type name 'u16'
  u16  transport_len; /* length of transport address */

Use __kernel_sa_family_t instead of sa_family_t the same way
as uapi/linux/in.h does, to fix the following
linux/rxrpc.h userspace compilation errors:

/usr/include/linux/rxrpc.h:23:2: error: unknown type name 'sa_family_t'
  sa_family_t srx_family; /* address family */
/usr/include/linux/rxrpc.h:28:3: error: unknown type name 'sa_family_t'
  sa_family_t family;  /* transport address family */

Fixes: 727f8914 ("rxrpc: Expose UAPI definitions to userspace")
Cc: <stable@vger.kernel.org> # v4.14
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: David S. Miller <davem@davemloft.net>