ixgbevf: Add flag to indicate when rx is in net poll

napi_gro_receive shouldn't be called from netpoll context.  Doing
so was causing kernel panics when jumbo frames larger than 2K were set.
Add a flag to check if the Rx ring processing is occurring from interrupt
context or from netpoll context and call netif_rx() if in the polling
context.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>