Try both fd and socket ops for net_read() and net_write()

Try both fd and socket ops for net_read() and net_write()

When using WinSock, a socket is not a file descriptor and does not
interoperate with read()/write().  File descriptors do not work with
send()/recv().  However, for net_read() and net_write(), we don't know
whether we are dealing with a socket or a file descriptor.  So try
one, and if it fails, try the other.

This is an ugly hack until we clean up the users of this API so it
doesn't use sockets and fds interchangably.