systemd-resolve: easy querying of TLSA records

systemd-resolve: easy querying of TLSA records

$ systemd-resolve --tlsa fedoraproject.org
_443._tcp.fedoraproject.org IN TLSA 0 0 1 GUAL5bejH7czkXcAeJ0vCiRxwMnVBsDlBMBsFtfLF8A=
        -- Cert. usage: CA constraint
        -- Selector: Full Certificate
        -- Matching type: SHA-256

$ systemd-resolve --tlsa=tcp fedoraproject.org:443
_443._tcp.fedoraproject.org IN TLSA 0 0 1 GUAL5bejH7czkXcAeJ0vCiRxwMnVBsDlBMBsFtfLF8A=
        ...

$ systemd-resolve --tlsa=udp fedoraproject.org
_443._udp.fedoraproject.org: resolve call failed: '_443._udp.fedoraproject.org' not found

v2:
- use uint16_t
- refuse port 0