net: introduce IPv4 IHL and version fields

net: introduce IPv4 IHL and version fields

RTE IPv4 header definition combines the `version' and `ihl'  fields
into a single structure member.
This patch introduces dedicated structure members for both `version'
and `ihl' IPv4 fields. Separated header fields definitions allow to
create simplified code to match on the IHL value in a flow rule.
The original `version_ihl' structure member is kept for backward
compatibility.

Signed-off-by: Gregory Etelson <getelson@nvidia.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Ray Kinsella <mdr@ashroe.eu>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>