Add per rule logging of dns_ssutable_checkrules processing

Add per rule logging of dns_ssutable_checkrules processing

These are logged to the update category at debug level 99 and
have the following form.

    update-policy: using: signer=ddns-key.example.nil, name=updated.example.nil, addr=10.53.0.1, tcp=0, type=A, target=
    update-policy: trying: grant zonesub-key.example.nil zonesub TXT
    update-policy: next rule: signer does not match identity
    update-policy: trying: grant ddns-key.example.nil zonesub ANY
    update-policy: matched: grant ddns-key.example.nil zonesub ANY

or

    update-policy: using: signer=restricted.example.nil, name=example.nil, addr=10.53.0.1, tcp=0, type=TXT, target=
    update-policy: trying: grant zonesub-key.example.nil zonesub TXT
    update-policy: next rule: signer does not match identity
    update-policy: trying: grant ddns-key.example.nil zonesub ANY
    update-policy: next rule: signer does not match identity
    update-policy: trying: grant restricted.example.nil zonesub ANY
    update-policy: next rule: name/subdomain mismatch
    update-policy: no match found

where 'using:' is the calling parameters of dns_ssutable_checkrules,
'trying:' in the rule bing evaluated, "next rule:" is the reason
the rule does not match, "matched:" repeats the matched rule, and
no match found is reported when te set of rules is exhausted.