IB/core: const'ify inbuf in struct ib_udata

Userspace input buffer is not modified by kernel, so it can be 'const'.

This is also a prerequisite to remove the implicit cast
from INIT_UDATA().

Link: http://marc.info/?i=cover.1386798254.git.ydroneaud@opteya.com>
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 979874c..61e1935 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -978,7 +978,7 @@
 };
 
 struct ib_udata {
-	void __user *inbuf;
+	const void __user *inbuf;
 	void __user *outbuf;
 	size_t       inlen;
 	size_t       outlen;