ixgbevf: fix jumbo frame

ixgbevf: fix jumbo frame

When latest Linux ixgbe PF is used, and DPDK VF is used in DPDK application,
jumbo frames are not received.
Also - if Linux ixgbe PF has MTU set to 1500 (default),
then normal sized packets can be received by DPDK VF.
However, if Linux PF has MTU > 1500, then DPDK VF receives no packets
(normal or jumbo).
With ixgbe_mbox_api_10 ixgbe simply didn't allow set VF MTU > 1514 for 82599.
With ixgbe_mbox_ajpi_11 it does, though now, if PF uses jumbo frames,
it simply disables RX for all VFs.
So to work with PF ithat using jumbo frames, at startup each VF has to:
1. negotiate with PF mbox_api_11.
2. Send to PF SET_LPE message with desired MTU.
Note, that if PF already uses MTU bigger then asked by the VF,
then PF wouldn't take any action.

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Ivan Boule <ivan.boule@6wind.com>