network: Use ff_neterrno instead of AVERROR(errno) for poll errors

This makes sure to pick up the actual error codes on windows.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/network.c

@@ -138,7 +138,7 @@ static int ff_poll_interrupt(struct pollfd *p, nfds_t nfds, int timeout,
     if (!ret)
         return AVERROR(ETIMEDOUT);
     if (ret < 0)
-        return AVERROR(errno);
+        return ff_neterrno();
     return ret;
 }