unix/moduselect: get_fd: Reintroduce fast path for file/socket objects.
unix/moduselect: get_fd: Reintroduce fast path for file/socket objects.

Majority of objects passed to uselect module would be normal file/socket
objects, so there was a fast path for then, not requiring to look up/call
virtual methods. It was removed in upstream commit ef554ef9a27, and this
commit reintroduces it again.

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython