ptrace: s/tracehook_tracer_task()/ptrace_parent()/

tracehook.h is on the way out.  Rename tracehook_tracer_task() to
ptrace_parent() and move it from tracehook.h to ptrace.h.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: John Johansen <john.johansen@canonical.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index a0d3845..fc07d18 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2048,7 +2048,7 @@
 			u32 ptsid = 0;
 
 			rcu_read_lock();
-			tracer = tracehook_tracer_task(current);
+			tracer = ptrace_parent(current);
 			if (likely(tracer != NULL)) {
 				sec = __task_cred(tracer)->security;
 				ptsid = sec->sid;
@@ -5314,7 +5314,7 @@
 		   Otherwise, leave SID unchanged and fail. */
 		ptsid = 0;
 		task_lock(p);
-		tracer = tracehook_tracer_task(p);
+		tracer = ptrace_parent(p);
 		if (tracer)
 			ptsid = task_sid(tracer);
 		task_unlock(p);