ah: Don't return NET_XMIT_DROP on input.

When the ahash driver returns -EBUSY, AH4/6 input functions return
NET_XMIT_DROP, presumably copied from the output code path.  But
returning transmit codes on input doesn't make a lot of sense.
Since NET_XMIT_DROP is a positive int, this gets interpreted as
the next header type (i.e., success).  As that can only end badly,
remove the check.

Signed-off-by: Nick Bowler <nbowler@elliptictech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>