seq_file: constify seq_operations

Make all seq_operations structs const, to help mitigate against
revectoring user-triggerable function pointers.

This is derived from the grsecurity patch, although generated from scratch
because it's simpler than extracting the changes from there.

Signed-off-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index 984a5eb..c1c9e03 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -1517,7 +1517,7 @@
 	return svc_export_show(m, &svc_export_cache, cp);
 }
 
-struct seq_operations nfs_exports_op = {
+const struct seq_operations nfs_exports_op = {
 	.start	= e_start,
 	.next	= e_next,
 	.stop	= e_stop,