Clearance of checksum flags when decapsulating ESP packets

[Dr. Rolf Jansen]

Please, may I ask about the rationale behind the lines 1557 to 1562 in function udp4_espdecap() of file src/sys/netinet/udp_usrreq.c on  FreeBSD 10.2-RELEASE-p3.

…
	/*
	 * We cannot yet update the cksums so clear any
	 * h/w cksum flags as they are no longer valid.
	*/
	 if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID)
		m->m_pkthdr.csum_flags &= ~(CSUM_DATA_VALID|CSUM_PSEUDO_HDR);
…

I am specially interested in learning about possibly adverse effects on operating an IPsec and IPsec-NAT-T enabled kernel when leaving the checksum flags in place, i.e. removing the above lines from the file src/sys/netinet/udp_usrreq.c.

Many thanks in advance for any enlightment.

Best regards

Rolf Jansen