ns: initialize nsid in rst_add_ns_id

Execute zdtm/live/static/pipe00
./pipe00 --pidfile=pipe00.pid --outfile=pipe00.out
Dump 3158
Restore
test/zdtm.sh: line 472:  3173 Segmentation fault      (core dumped) setsid  restore --file-locks --tcp-established -x -D  -o

Reported-by: Jenkins Criuovich
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>