e1000e: consistent use of Rx/Tx vs. RX/TX/rx/tx in comments/logs

Some minor comment errors and whitespace issues discovered while looking
into this are also addressed.

Signed-off-by: Bruce 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>