Unlike CPython socket, microsocket object already implements stream protocol
(read/write methods), so makefile() just returns object itself. TODO: this
doesn't take care of arguments CPython's makefile() may accept.

Implementation is duplicated, but tolerate this for now, because there's
no clear idea how to de-dup it.

It's no longer intended to provide just "raw" socket interface, may include
some convenience methods for compatibility with CPython socket - but anyway
just minimal set required to deal with socket client and servers, not wider
network functionality.

Can't decide which is better for string type, char or byte pointer.
Changing to char removes a few casts.  Really need to do proper unicode.

-147 bytes on x86.

Can now have null bytes in strings.  Can define ROM qstrs per port using
qstrdefsport.h

CPython _socket actually have only those and doesn't provide stream
interface (higher-level CPython "socket" what adds this).

+516 bytes x86.