Line endings, encoding, negative ifreq

[makrohard]

After using this great streight-forward script for years, it did not work anymore on a new system, using Gqrx 2.17.5 and Python 3.12.6.

I added a Pull request that changed the script:

• Adding line endings \r\n to the data send to Gqrx made the script work again. \n only also worked, but \r\n seemed to me more interoperable

• Specified utf-8 encoding explicitly to the send lines (can't hurt, can it?)

• Finally, I have to use swap i/o in combination with a negative ifreq in order to get the frequency synced correctly. The script assumes positive ifreq, thus the calculations were wrong. I added a condition that checks is ifreq is positive or negative and does the calculations accordingly.