ibmveth: Remove LLTX

The ibmveth adapter needs locking in the transmit routine to protect
the bounce_buffer but it sets LLTX and forgets to add any of its own
locking.

Just remove the deprecated LLTX option. Remove the stats lock in the process.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Santiago Leon <santil@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>