net/enic: use TSO flags
net/enic: use TSO flags

Depend on the tx_offload flags in the mbuf to determine the length
of the headers instead of looking into the packet itself.

Signed-off-by: John Daley <097981eb5abe5dbeac3142a4f5a88742d916de86@cisco.com>
Reviewed-by: Hyong Youb Kim <410cadac1eb3154f1b3752aedc2559ad69f3863e@cisco.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk