e1000e: cosmetic cleanup of comments

Update comments to conform to the preferred style for networking code as
described in ./Documentation/CodingStyle and checked for in the recently
added checkpatch NETWORKING_BLOCK_COMMENT_STYLE test.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>