In server, treat a purported client IP address of 0.0.0.0 as missing

In #33157 (moved), proxies sometimes fail to extract a meaningful client IP address from the client's SDP and send ?client_ip=0.0.0.0 to the bridge. The bridge counts an address of 0.0.0.0 as a client that had an IP address, which inflates the numerator in the "in the past %.f s, %d/%d connections had client_ip" log line.

This is a patch to treat a client address of 0.0.0.0 or [::] as if it were not present at all.