The function rte_ipv4_udptcp_cksum (and probably also
rte_ipv4_udptcp_cksum_verify ) does not work properly when the header is taken
from a mbuf that consist of multiple segments.

I suggest editing the documentation to say e.g. "if the header is taken from a
mbuf with e.g. rte_pktmbuf_mtod which potentially consist of multiple segments,
use rte_ipv4_udptcp_cksum_mbuf instead."

Related:
https://inbox.dpdk.org/dev/20211015051306.320328-1-xiaoyun.li@intel.com/T/