kernel/fork.c:copy_process(): unify CLONE_THREAD-or-thread_group_leader code

kernel/fork.c:copy_process(): unify CLONE_THREAD-or-thread_group_leader code

Cleanup and preparation for the next changes.

Move the "if (clone_flags & CLONE_THREAD)" code down under "if
(likely(p->pid))" and turn it into into the "else" branch.  This makes the
process/thread initialization more symmetrical and removes one check.

Signed-off-by: Oleg Nesterov <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Sergey Dyasly <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>