ixgbe: remove redundant configuration of vmolr, rename generic variable

The vmolr is configured already in ixgbe_set_rx_mode for the PF so there is
no need to set it again in ixgbe_configure_rx.

Instead of using the variable name reg, it is easier to just rename it to
gcr_ext to reflect the register contents that the variable holds.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>