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 <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/uapi/linux/llc.h

···
 #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 {