net: Really remove all of LOOPBACK_TSO code.

As noticed by Saikiran Madugula, commit 7447ef63
("loopback: Remove rest of LOOPBACK_TSO code.") got rid of
emulate_large_send_offload() but didn't get rid of the call
site as well.

Signed-off-by: David S. Miller <davem@davemloft.net>