IPC - Socket Thread not captured under Networking settings

I am debugging a networking issue (https://bugzilla.mozilla.org/show_bug.cgi?id=1806942) in Firefox which can be demonstrated using https://packetlosstest.com/. That site uses a WebRTC stream to measure latency and packet loss. The specific issue is that the latency goes high and variable on a periodic basis, roughly for 1 second every 6 seconds. When capturing with all or nearly-all threads, the high latency time periods are visible in the IPC -- Socket Thread chart, e.g. in https://share.firefox.dev/3LQwYBy looking at the time period from 10.5s to 13.25 seconds you can see that the arrival times of IPCs on the socket thread are less regular. It's also less regular at two other periods. During those segments of the profile, the latency in the WebRTC test also shows as being high, as you can see in the final screenshot from the full time period.

But when capturing with Networking settings https://share.firefox.dev/3TQJz9Y, the issue is not visible in the chart - from 10.3s through 11.15s it is happening during this profile, but it's not captured.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-625)