ixgbevf: Move Tx clean-up into NAPI context

Currently the VF driver is processing all of the transmits in interrupt
context.  This can be messy since the Rx is all handled in NAPI and this
may result in interrupts being disabled.  In order to resolve this move all
of the Tx packet processing into NAPI and combine all of the interrupt and
polling routines into just a pair of functions.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
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>