Baud selector jumps back to previous value if port changed

I've found that if I change the Baud rate (from say 57600 to 115200) and then change the port the baud rate reverts to the previous value

Reproduce the issue by changing the baud rate from 57600 to 115200, then changing the port, and observe whether the baud rate reverts. Trace the Mission Planner port and baud selector handling; done means the selected baud rate remains unchanged after the port changes.

Written by the indexing model from the issue text.