RDMA/nes: Remove LLTX

NETIF_F_LLTX is deprecated. Remove private TX locking from the driver
and remove the NETIF_F_LLTX feature flag.  This also fixes a warning
in some configs that comes from doing skb_linearize() call in the
hard_start_xmit method with IRQs disabled (if HIGHMEM is enabled,
skb_linearize() may end up enabling BHs, which is a no-no if hard IRQs
are disabled in that context).  By getting rid of LLTX, we do not
disable IRQs when skb_linearize() is called.

Remove the sq_lock as it is not needed for non-LLTX.  Fix ethtool not
to show the counter for sq_lock.

Reported-by:  <aluno3@poczta.onet.pl>
Signed-off-by: Faisal Latif <faisal.latif@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>