ixgbe: cleanup feature flags in ixgbe_probe

I'm removing NETIF_F_GRO from being initialed in the feature flags during
ixgbe_probe() bases on a comment from Michal Miroslaw
<mirq-linux@rere.qmqm.pl> that it is always set by network code now.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>