vmxnet3: support jumbo frames

vmxnet3: support jumbo frames

Add support for linking multi-segment buffers together to
handle Jumbo packets. The vmxnet3 API supports having header
and body buffer types. What this patch does is fill the primary
ring completely with header buffers and the secondary ring
with body buffers. This allows for non-jumbo frames to only
use one mbuf (from primary ring); and jumbo frames will have
first mbuf from primary ring and following mbufs from other
ring.

This could be optimized in future if the DPDK had API
to supply different sized mbufs (two pools) into driver.

Signed-off-by: Stephen Hemminger <shemming@brocade.com>
Acked-by: Remy Horton <remy.horton@intel.com>
Release note addition:
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>