mediaextractor: allow rt_sigprocmask syscall

Change-Id: I551b34565305bb72a105789a29f9793cbd653ad1
diff --git a/services/mediaextractor/minijail/seccomp_policy/mediaextractor-seccomp-arm.policy b/services/mediaextractor/minijail/seccomp_policy/mediaextractor-seccomp-arm.policy
index 47d6216..e3ac507 100644
--- a/services/mediaextractor/minijail/seccomp_policy/mediaextractor-seccomp-arm.policy
+++ b/services/mediaextractor/minijail/seccomp_policy/mediaextractor-seccomp-arm.policy
@@ -30,3 +30,4 @@
 brk: 1
 sched_setscheduler: 1
 gettid: 1
+rt_sigprocmask: 1