uml: fix mconsole stop

Bring back the functionality of stopping user mode linux with the help of
mconsole.

[jdike - the bug being fixed is that the mconsole file descriptor is already
set O_NONBLOCK or not, depending on whether we want no blocking (the normal
case) or we want blocking (when an mconsole stop is in effect), so the
MSG_DONTWAIT is redundant in the normal case, and wrong when we want to
block.]

Signed-off-by: Karol Swietlicki <magotari@gmail.com>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/drivers/mconsole_user.c

@@ -83,9 +83,8 @@ int mconsole_get_request(int fd, struct mc_request *req)
 	int len;
 
 	req->originlen = sizeof(req->origin);
-	req->len = recvfrom(fd, &req->request, sizeof(req->request),
-			    MSG_DONTWAIT, (struct sockaddr *) req->origin,
-			    &req->originlen);
+	req->len = recvfrom(fd, &req->request, sizeof(req->request), 0,
+			    (struct sockaddr *) req->origin, &req->originlen);
 	if (req->len < 0)
 		return 0;