uapi: fix linux/ip6_tunnel.h userspace compilation errors

Include <linux/if.h> and <linux/in6.h> to fix the following
linux/ip6_tunnel.h userspace compilation errors:

/usr/include/linux/ip6_tunnel.h:23:12: error: 'IFNAMSIZ' undeclared here (not in a function)
char name[IFNAMSIZ]; /* name of tunnel device */
/usr/include/linux/ip6_tunnel.h:30:18: error: field 'laddr' has incomplete type
struct in6_addr laddr; /* local tunnel end-point address */

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

include/uapi/linux/ip6_tunnel.h

···
 #define _IP6_TUNNEL_H
 
 #include <linux/types.h>
+#include <linux/if.h>		/* For IFNAMSIZ. */
+#include <linux/in6.h>		/* For struct in6_addr. */
 
 #define IPV6_TLV_TNL_ENCAP_LIMIT 4
 #define IPV6_DEFAULT_TNL_ENCAP_LIMIT 4