alloc_percpu: add align argument to __alloc_percpu.

This prepares for a real __alloc_percpu, by adding an alignment argument.
Only one place uses __alloc_percpu directly, and that's for a string.

tj: af_inet also uses __alloc_percpu(), update it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blktrace.c b/block/blktrace.c
index 39cc3bf..4877662 100644
--- a/block/blktrace.c
+++ b/block/blktrace.c
@@ -363,7 +363,7 @@
 	if (!bt->sequence)
 		goto err;
 
-	bt->msg_data = __alloc_percpu(BLK_TN_MAX_MSG);
+	bt->msg_data = __alloc_percpu(BLK_TN_MAX_MSG, __alignof__(char));
 	if (!bt->msg_data)
 		goto err;