Fix mode switching by replacing rig_parse_mode with RIG_MODE_* mapping

[N1RX]

Hi F4HTB,

while setting up a new Docker container, I ran into an issue where Hamlib.rig_parse_mode wasn't available in the Python bindings.

This small change replaces it with a direct mapping to Hamlib.RIG_MODE_* constants. It fixes the issue for me and should make the code more robust across different environments.

Tested and working with all modes.

73 de DL3NW

[F4HTB]

Hello Dear,

Thanks for pushing some code. As you can see rig_parse_mode alwais exist: https://github.com/Hamlib/Hamlib/blob/master/include/hamlib/rig.h

I prefer not to downgrade this and use this function of hamlib. Can you tell me the version of hamlib used in your project?

73!