Lots of fixes to com port option handling

[larsks]

Hey folks,

I'm using esp-link to remotely debug the Linux kernel on a raspberry pi. To get things working I needed to correct several issues with the com port options handling (RFC 2217). You can find my changes here:

• https://github.com/larsks/esp-link

The current commit log looks like this:

• 11bdf66 Send correct response to RFC 2217 SET-BAUDRATE command
• b1b8758 Send correct response to RFC 2217 SET-PARITY command
• ae19fcd Handle RFC 2217 SET-CONTROL flow control options
• 15f57db Handle RFC 2217 SET-STOPSIZE requests
• ed435bf Handle RFC 2217 SIGNATURE command
• 5d185c1 Handle telnet DO command
• 997705c Handle telnet BREAK command
• e95433d Ignore unknown telnet commands
• 83a8aed Increase serial server timeout

I would normally submit pull requests against the upstream repository, but it looks like this repository has been abandoned. I am happy to collect patches in my fork if folks want to submit them there.