ixgbe/base: enable X550 FEC when EEE is disabled

ixgbe/base: enable X550 FEC when EEE is disabled

The FEC(Forward Error Correction) feature had been disabled
because it increases power consumption. However, some customers
want to use it. This patch enables FEC when EEE(Energy Efficient
Ethernet) is disabled; FEC was already being disabled when EEE
was enabled, but now both are done in the same function. The two
features are not allowed to be enabled at the same time. The two
features cannot both be disabled. If this ability is ever
determined to be needed, we will need to define a new user parameter
to control FEC independently of EEE.

Fixes: d4c9ffd4fe1c ("ixgbe/base: disable X550em FEC to save power")

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: Helin Zhang <helin.zhang@intel.com>