staging: hv: fix netvsc sleeping while atomic

commit d70c673153 upstream.

The channel callbacks are called directly from vmbus_event_dpc
which runs in tasklet context. These callbacks need to use
GFP_ATOMIC.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=16701

Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/hv/netvsc.c

@@ -1236,7 +1236,7 @@ static void NetVscOnChannelCallback(void *Context)
 	/* ASSERT(device); */
 
 	packet = kzalloc(NETVSC_PACKET_SIZE * sizeof(unsigned char),
-			 GFP_KERNEL);
+			 GFP_ATOMIC);
 	if (!packet)
 		return;
 	buffer = packet;