vr_host_interface.c: skb->rxhash renamed in EL7.2
vr_host_interface.c: skb->rxhash renamed in EL7.2

EL7.2 has integrated the upstream (torvalds/linux.git) commit 61b905da33
that renames skbuff's "rxhash" member into "hash".

There are two functions in vr_host_interface.c that relies on the
skb->rxhash member: vr_skb_set_rxhash and vr_skb_get_rxhash.

These two functions already carry tests:
 - tests that Linux version is between 2.6.32 and 3.15.0
   (skb->rxhash is the correct name in this region)
 - tests that, when the above is true, RHEL (major,minor) is at least (6,4)

We're adding another test to declare that when Linux version is greater
than 3.15.0, and:
 - a) RHEL (major,minor) is greater than (7,2), use skb->hash,
 - b) else, use skb->rxhash.

Compilation of vrouter then succeeds on EL 7.2 again, and sends
packets.

Change-Id: Id70126356293bc08058db10f3ef5005bbd1a1899
Closes-Bug: #1531237
Signed-off-by: Martin Millnert <54669547a225ff20cba8b75a4adca540eef25858@millnert.se>

codilime/contrail-vrouter,codilime/contrail-vrouter,codilime/contrail-vrouter,codilime/contrail-vrouter