Phonet: include generic link-layer header size in MAX_PHONET_HEADER

This fixes an OOPS in hard_header if a Phonet address is assigned to a
non-Phonet network interface.
Signed-off-by: Remi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/phonet/phonet.h

@@ -27,7 +27,7 @@
  * The lower layers may not require more space, ever. Make sure it's
  * enough.
  */
-#define MAX_PHONET_HEADER	8
+#define MAX_PHONET_HEADER	(8 + MAX_HEADER)
 
 /*
  * Every Phonet* socket has this structure first in its