netfilter: bridge: kill nf_bridge_pad

The br_netfilter frag output function calls skb_cow_head() so in
case it needs a larger headroom to e.g. re-add a previously stripped PPPOE
or VLAN header things will still work (at cost of reallocation).

We can then move nf_bridge_encap_header_len to br_netfilter.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index a7aea20..90b49e8 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -636,10 +636,7 @@
 	left = skb->len - hlen;		/* Space per frame */
 	ptr = hlen;		/* Where to start from */
 
-	/* for bridged IP traffic encapsulated inside f.e. a vlan header,
-	 * we need to make room for the encapsulating header
-	 */
-	ll_rs = LL_RESERVED_SPACE_EXTRA(rt->dst.dev, nf_bridge_pad(skb));
+	ll_rs = LL_RESERVED_SPACE(rt->dst.dev);
 
 	/*
 	 *	Fragment the datagram.