include/uapi/linux/socket.h: include sys/socket.h in userspace

This libc header has sockaddr definition for userspace.

Fixes userspace compilation errors like these from kernel headers including
only linux/socket.h:

error: field ‘ifru_addr’ has incomplete type
struct sockaddr ifru_addr;

Signed-off-by: Mikko Rapeli <redacted>
---
 include/uapi/linux/socket.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/uapi/linux/socket.h b/include/uapi/linux/socket.h
index 76ab0c6..8a81197 100644
--- a/include/uapi/linux/socket.h
+++ b/include/uapi/linux/socket.h

@@ -1,6 +1,10 @@
 #ifndef _UAPI_LINUX_SOCKET_H
 #define _UAPI_LINUX_SOCKET_H
 
+#ifndef __KERNEL__
+#include <sys/socket.h>
+#endif
+
 /*
  * Desired design of maximum size and alignment (see RFC2553)
  */

-- 
2.1.4