Fix icmp checksum when sequence number modlation is being used. Also fix a daddr vs saddr cut-n-paste error in ICMP error handling.
Fix icmp checksum when sequence number modlation is being used.
Also fix a daddr vs saddr cut-n-paste error in ICMP error handling.

From dhartmei@
ok deraadt@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars