- Update the Intel Wired LAN documentation with the latest
  URL for ethtool.

- replace "Ethtool" with "ethtool"
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: NEmil Tantilov <emil.s.tantilov@intel.com>

Update Intel Wired LAN igb documentation.

v2- Updated the ethtool support link, removed the LRO section and
    anti-spoofing sections.
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

Add documentation for the igb networking driver.

  v2:
   - Removed trailing white space
   - Removed Ethtool version info
   - Removed LRO kernel version info
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: NJeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>