Return correct errno in raspberrypi's Socket.c

[georgboe]

This PR fixes #6988

Changes seems to have been made in ca9523b to address this, but it is still wrong.

ret is defined as mp_uint_t and is therefore never less than zero, this uses the same solution as line 1060 in the same file.
Also the value in received is now a negative number, and must be converted to a positive number before being raised to match up with errno.ETIMEDOUT and errno.EAGAIN.

[jepler]

Thanks, this looks sensible. Clearly my own change lacked clarity and testing. Please ping me when you're ready to take this out of 'draft' status!

[georgboe]

@jepler Thank you, I have set it as "Ready for review" now.

[dhalbert]

@jepler Strangely, the CI is building all the espressif boards as well as the raspberrypi boards.