fw-dump: add openat to seccomp

This adds openat to a seccomp policy file if open is already there.
We need this because glibc 2.25 changed it system call for open().

BUG=chromium:894614
TEST=None

Change-Id: I1208ac922a8b8d5c7f91c0d15fa89afdb8bd1b15
Reviewed-on: https://chrome-internal-review.googlesource.com/701350
Commit-Ready: Yunlian Jiang <yunlian@google.com>
Tested-by: Yunlian Jiang <yunlian@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/intel-wifi-fw-dump/+/1925479
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Kirtika Ruchandani <kirtika@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/sandbox/fw_parser-seccomp.policy b/sandbox/fw_parser-seccomp.policy
index f1c0d66..8b5d68a 100644
--- a/sandbox/fw_parser-seccomp.policy
+++ b/sandbox/fw_parser-seccomp.policy
@@ -18,6 +18,7 @@
 mremap: 1
 munmap: 1
 open: 1
+openat: 1
 read: 1
 stat: 1
 write: 1