net: calculate checksum of packet with IPv4 options

net: calculate checksum of packet with IPv4 options

Currently, rte_ipv4_cksum() and rte_ipv4_udptcp_cksum() assume all IPv4
headers have sizeof(struct rte_ipv4_hdr) bytes. This is not true for
those (rare) packets with IPv4 options. Thus, both IPv4 and TCP/UDP
checksums are calculated wrong.

This patch fixes the issue by using the actual IPv4 header length from
the packet's IHL field.

Signed-off-by: Michael Pfeiffer <michael.pfeiffer@tu-ilmenau.de>
Reviewed-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>