net: smc91c111: guard flush_queued_packets() on can_rx()

Check that the core can once again receive packets before asking the
net layer to do a flush. This will make it more convenient to flush
packets when adding new conditions to can_receive.

Add missing if braces while moving the can_receive() core code.

Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Tested-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Message-id: 92e15e12a6964274f4bc0eb71b61a7d94326f6c6.1441873621.git.crosthwaite.peter@gmail.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>