The qemu_*block() functions are meant to be be used with sockets (the
win32 implementation expects SOCKET)

Over time, those functions where used with Win32 SOCKET or
file-descriptors interchangeably. But for portability, they must only be
used with socket-like file-descriptors. FDs can use
g_unix_set_fd_nonblocking() instead.

Rename the functions with "socket" in the name to prevent bad usages.

This is effectively reverting commit f9e8cacc ("oslib-posix:
rename socket_set_nonblock() to qemu_set_nonblock()").

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>