bonding: Return pointer to data after pull on skb

Since 429e3d12 ("bonding: Fix extraction of ports from the packet
headers"), header offsets used to compute a hash in bond_xmit_hash() are
relative to skb->data and not skb->head. If the tail of the header buffer
of an skb really needs to be advanced and the operation is successful, the
pointer to the data must be returned (and not a pointer to the head of the
buffer).

Fixes: 429e3d12

 ("bonding: Fix extraction of ports from the packet headers")
Signed-off-by: Jiri Wiesner <jwiesner@suse.de>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>