bridge: Clear INET control block of SKBs passed into ip_fragment().

In a similar vain to commit 17762060
("bridge: Clear IPCB before possible entry into IP stack")

Any time we call into the IP stack we have to make sure the state
there is as expected by the ipv4 code.

With help from Eric Dumazet and Herbert Xu.

Reported-by: Bandan Das <bandan.das@stratus.com>
Signed-off-by: David S. Miller <davem@davemloft.net>