tipc: make sure IPv6 header fits in skb headroom

Expand headroom further in order to be able to fit the larger IPv6
header. Prior to this patch this caused a skb under panic for certain
tipc packets when using IPv6 UDP bearer(s).
Signed-off-by: Richard Alpe <richard.alpe@ericsson.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/udp_media.c

@@ -53,7 +53,7 @@
 /* IANA assigned UDP port */
 #define UDP_PORT_DEFAULT	6118
 
-#define UDP_MIN_HEADROOM        28
+#define UDP_MIN_HEADROOM        48
 
 /**
  * struct udp_media_addr - IP/UDP addressing information