lsm: cleanup the size counters in security_getselfattr()

Zero out all of the size counters in the -E2BIG case (buffer too
small) to help make the current code a bit more robust in the face of
future code changes.
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/security.c

@@ -3950,8 +3950,9 @@ int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
 			continue;
 		}
 		if (rc == -E2BIG) {
-			toobig = true;
+			rc = 0;
 			left = 0;
+			toobig = true;
 		} else if (rc < 0)
 			return rc;
 		else