MFC r271978

ipfilter bug #552 destination port not zero after parsing nat rule.

Obtained from:	netbsd CVS repo (r1.4), ipfilter CVS repo (r1.38)
MFC r271980

Check for NULL before de-refencing; in particular sel is assigned to NULL,
in the default case, and then couple of lines down we do sel->

Obtained from:	NetBSD CVS repo (r1.5)
MFC r272052

ipfilter bug #558 add in some missing frag table function comments.

Obtained from:	ipfilter CVS repo (r1.36)
MFC r272551

ipfiler bug #550 filter rule list corrupted with inserted rules

Obtained from:	ipfilter CVS repo (r1.128); NetBSD CVS repo (r1.15)
MFC r272552

ipfilter bug #554 Determining why a ipf rule matches is hard -- replace
ipfilter rule compare with new ipf_rule_compare() function.

Obtained from:	ipfilter CVS rep (r1.129)
MFC r272553

ipfilter bug #538 ipf_p_dns_del should return void

Obtained from:	ipfilter cvs repo (r1.8)
MFC r272554

ipfilter bug #534 destination list hashing not endian neutral

Obtained from:	ipfilter CVS repo (r1.26), NetBSD CVS repo (r1.8)
MFC r272555

ipfilter bug #537 NAT rules with sticky have incorrect hostmap IP address.
This fixes when an IP address mapping is put in the hostmap table for
sticky NAT rules, it ends up having the wrong byte order.

Obtained from:	ipfilter CVS repo (r1.102), NetBSD CVS repo (r1.12)