uapi: fix linux/llc.h userspace compilation error

Include <linux/if.h> to fix the following linux/llc.h userspace
compilation error:

/usr/include/linux/llc.h:26:27: error: 'IFHWADDRLEN' undeclared here (not in a function)
  unsigned char   sllc_mac[IFHWADDRLEN];
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/llc.h

@@ -14,6 +14,7 @@
 #define _UAPI__LINUX_LLC_H
 
 #include <linux/socket.h>
+#include <linux/if.h> 		/* For IFHWADDRLEN. */
 
 #define __LLC_SOCK_SIZE__ 16	/* sizeof(sockaddr_llc), word align. */
 struct sockaddr_llc {