e1000e: drop lltx, remove unnecessary lock

LLTX is deprecated and complicated, don't use it.  It was observed by Don Ash
<donash4@gmail.com> that e1000e was acquiring this lock in the NAPI cleanup
path.  This is obviously a bug, as this is a leftover from when e1000
supported multiple tx queues and fake netdevs.

another user reported this to us and tested routing with the 2.6.27 kernel and
this patch and reported a 3.5 % improvement in packets forwarded in a
multi-port test on 82571 parts.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>