Jan Kiszka authored Mar 08, 2018 and Philippe Gerum committed Mar 14, 2018

This both de-duplicates the code and ensures that all fields are zeroed
prior to calling one of the actual tcb initialization functions.
Specifically if host_task is not properly cleaned, we may cause a bug
when using the field earlier, e.g.

general protection fault: 0000 [#1] PREEMPT SMP
[...]
RIP: 0010:[<ffffffff81185a3c>]  [<ffffffff81185a3c>] xnthread_host_pid+0x1c/0x30
[..]
Call Trace:
 [<ffffffff8117c987>] trace_event_raw_event_cobalt_thread_set_current_prio+0x57/0xa0
 [<ffffffff8117f33d>] xnsched_set_effective_priority+0x8d/0xc0
 [<ffffffff8117a1e4>] xnsched_rt_setparam+0x14/0x30
 [<ffffffff8117e700>] xnsched_set_policy+0xc0/0x170
 [<ffffffff81185687>] __xnthread_init+0x317/0x3d0
 [<ffffffff8114a3e8>] ? trace_buffer_unlock_commit+0x58/0x70
 [<ffffffff811857bb>] xnthread_init+0x7b/0x110

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>