MFC r345366:

MFC r345366:

pf: Ensure that IP addresses match in ICMP error packets

States in pf(4) let ICMP and ICMP6 packets pass if they have a
packet in their payload that matches an exiting connection.  It was
not checked whether the outer ICMP packet has the same destination
IP as the source IP of the inner protocol packet.  Enforce that
these addresses match, to prevent ICMP packets that do not make
sense.

Reported by:	Nicolas Collignon, Corentin Bayet, Eloi Vanderbeken, Luca Moro at Synacktiv
Obtained from:	OpenBSD
Security:	CVE-2019-5598