sunvnet: hack to work around Solaris VIO bug

sunvnet: hack to work around Solaris VIO bug

Orabug 21895216

port workaround used for Bug 20455702:

This patch works around a problem where Solaris drops packets bound for
physical NICs (i.e., off host) that are using LSO and do not have the VIO v7
descriptor flags VNET_PKT_HASH, VNET_PKT_HCK_IPV4_HDRCKSUM,
VNET_PKT_HCK_FULLCKSUM set along with VNET_PKT_IPV4_LSO.

This patch can't go upstream because it doesn't actually support output
hashing (all packets will hash to '0'). The full and IPv4 header checksum
computations caused by the flags are unnecessary for Linux, but only affect
destinations through the vswitch.
(cherry picked from commit 3839694e54df457997025775894f954ea3185aff)