Add a function to calculate the length of an IPv4 header as suggested
on the mailing list [1]. Call where appropriate.
[1] https://mails.dpdk.org/archives/dev/2020-October/184471.html
Suggested-by: Thomas Monjalon <thomas@monjalon.net>
Signed-off-by: Michael Pfeiffer <michael.pfeiffer@tu-ilmenau.de>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>