UPSTREAM: arm64/ptrace: run seccomp after ptrace

Close the hole where ptrace can change a syscall out from under seccomp.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
(cherry picked from commit a5cd110cb8369d6b37ef5ccfe56b3fa1338c9615)

Bug: 119769499
Change-Id: I9fd3e8e6d38122866df434b2676bf7ba0e808e32
Signed-off-by: Greg Hackmann <ghackmann@google.com>