e1000e: Fix Explicitly set Transmit Control Register

This patch causes the TCTL to be explicitly set to fix a problem with
poor network performance (throughput) on certain silicon when configured
for 100M HDX performance.

Cc: Todd Fujinaka <todd.fujinaka@intel.com>
Signed-off-by: Dave Ertman <davidx.m.ertman@intel.com>
Acked-by: Bruce W. Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>