ixgbe: Cleanup on the Rx init path

This cleans up the following pieces of the Rx initialization path:

- Enable the ECC memory fault interrupt in OTHER causes.

- Fix an 82598 initialization of RDRXCTL when depending on RSS and VMDq to
be enabled.  We don't need these features enabled to safely set the MVMEN
bit to allow multiple SRRCTL register mappings into the RXDCTL registers.

- Fix the RSS initialization path to not stomp on DCB accidentally.  When
configuring the MRQC (multiple Rx queue contol) register, we want to make
sure we only OR in features as necessary, instead of full assignment.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>