[SK_BUFF]: export skb_pull_rcsum

*** Warning: "skb_pull_rcsum" [net/bridge/bridge.ko] undefined!
*** Warning: "skb_pull_rcsum" [net/8021q/8021q.ko] undefined!
*** Warning: "skb_pull_rcsum" [drivers/net/pppoe.ko] undefined!
*** Warning: "skb_pull_rcsum" [drivers/net/ppp_generic.ko] undefined!

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>