ixgbevf: Make sure jumbo frames are set correctly after PF reset

If the Physical Function (PF) resets after the VF has set jumbo
frame MTU then the VF jumbo frame is overwritten.  Make sure the
VF driver always requests proper MTU size after reset
synchronization.

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>