ixgbevf: add check for CHECKSUM_PARTIAL when doing TSO

This patch adds check for CHECKSUM_PARTIAL to avoid the skb_is_gso check
in ixgbevf_tso(). It should reduce overhead for workloads that are not using
TSO or checksum offloads. It is the same as in ixgbe.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>