ixgbe: IXGBE_RXD_STAT_VP set even with Rx stripping enabled

The hardware bit IXGBE_RXD_STAT_VP appears to be set even when Rx
stripping is disabled. This results in passing frames up the stack
which do not have the 802.1Q tag stripped but have the tci bits
set as if it was.

Working around this with a check for the feature flag bit. I
would welcome any better ideas or a pointer to exactly which
bits in the hardware register need to be cleared to get the
IXGBE_RXD_STAT_VP bit to be set per data sheet.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Marcus Dennis <marcusx.e.dennis@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>