ptrace: Always take siglock in ptrace_resume

Make code analysis simpler and future changes easier by
always taking siglock in ptrace_resume.

Tested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lkml.kernel.org/r/20220505182645.497868-11-ebiederm@xmission.com


Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>