src/usr/lib/xymon/client/ext/dnsq: use rdstring instead of rdatastr

This fixes a deprecation warning in the dnsq status message.

Should work with Net::DNS >= 1.01, at least when I believe https://github.com/fastmail/authentication_milter/pull/141/files. I didn't find it in https://metacpan.org/dist/Net-DNS/changes . ;-)

Ubuntu 24.04 (NET:DNS 1.44) shows a deprecation warning in the "dnsq" status message:

yellow Warning: deprecated method; prefer $rr->rdstring() at /usr/lib/xymon/client/ext/dnsq line 63.

This is the patch that fixed it for me.

At least with NET:DNS <= 1.36 this warning isn't shown.

https://metacpan.org/dist/Net-DNS/changes shows it was deprecated in NET:DNS 1.38.

As far as I can see Debian Sid already contains NET:DNS 1.48 (https://packages.debian.org/sid/libnet-dns-perl) so this IMHO should also be affected.

Kind regard Lars