net/ixgbe: set min and max MTU for VF

net/ixgbe: set min and max MTU for VF

This commit sets the min and max supported MTU values for ixgbe VF
devices via the ixgbevf_dev_set_mtu() function. Min MTU supported is
set to ETHER_MIN_MTU and max MTU is calculated as the max packet length
supported minus the transport overhead. As transport overhead is the
same for VF and PF ixgbe devices, reuse MACRO 'IXGBE_ETH_OVERHEAD' to
avoid duplication.

Signed-off-by: Ian Stokes <ian.stokes@intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>