Allow disabling of automatic chan_sip port changes

We're just moving to Asterisk 16 and are looking at moving to chan_pjsip. For various reasons, we are not moving our trunks over right away, and wanted to have both drivers in place simultaneously for a time. However, the port number wants to be changed, making this more difficult than it needs to be. I would like to make the decision for my system whether or not it running different drivers on different interfaces is "just going to be a nightmare" (per comments in the code.)

Adding an advanced settings would be an easy fix for this; I'll submit a pull request if it will be accepted.