Temporarily disable setting seccomp filters in Minijail.

To make merging the BPF-based seccomp filter implementation easier,
turn off setting seccomp filters in Minijail. Add a flag ("-F") to
force setting seccomp filters.

BUG=chromium-os:27878
TEST=security_Minijail0 still passes.

Change-Id: I1948223f2292cf5c059bf50f69fd0b4e42ec39a2
Reviewed-on: https://gerrit.chromium.org/gerrit/21170
Commit-Ready: Jorge Lucangeli Obes <jorgelo@chromium.org>
Tested-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Will Drewry <wad@chromium.org>
diff --git a/libminijail.h b/libminijail.h
index e3828af..5753196 100644
--- a/libminijail.h
+++ b/libminijail.h
@@ -44,6 +44,7 @@
 int minijail_change_group(struct minijail *j, const char *group);
 void minijail_use_seccomp(struct minijail *j);
 void minijail_use_seccomp_filter(struct minijail *j);
+void minijail_force_seccomp_filter(struct minijail *j);
 void minijail_parse_seccomp_filters(struct minijail *j, const char *path);
 int minijail_add_seccomp_filter(struct minijail *j, int nr,
 				const char *filter);