Update dplatform_unix.py to allow bluetooth serial device selection o…

[ioClarity]

I understand this version is no longer supported, but this extremely small change to the user interface allows for selections of serial bluetooth connections (on Linux). For example, bluetooth serial connections to iCom 4100's and the like are presented to the OS like this (or at least on Debian 13)

• Added /dev/rfcomm* devices to selection list (serial devices over bluetooth connections present this way in linux)

[wb8tyw]

This version is still being supported, a newer version is in development, but it will be a while before it is usable.

This PR is https://github.com/ham-radio-software/D-Rats/pull/308/files is related to this PR as is ticket https://github.com/ham-radio-software/D-Rats/issues/309