syscall_filter: Implement flag set inclusion.

When filtering syscalls that take flags as an argument, we usually want
to allow a small set of "safe" flags. This is hard to express with the
current language.

Implement this by adding a "flag set inclusion" mode using the 'in'
keyword. This works by allowing the syscall as long as the passed
flags, when viewed as a set, are included in the set of flags described
by the policy.

Also, clang-format all of bpf.c.

Bug: 31997910
Test: syscall_filter_unittest
Change-Id: I121af56b176bd3260904d367fd92d47a16bb3dcb
6 files changed