net: define IPv4 IHL and VHL

net: define IPv4 IHL and VHL

Define IPv4 Minimum IHL and VHL according to rfc791 (see [1])

    "The Version field indicates the format of the
    internet header."

    "Internet Header Length (ihl) is the length of the
    internet header in 32 bit words, and thus points
    to the beginning of the data. Note that
    the minimum value for a correct header is 5."

[1] https://tools.ietf.org/html/rfc791

Signed-off-by: Saleh Alsouqi <salehals@mellanox.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>