fix(ssl): init peer_id when init tls_multi

fix(ssl): init peer_id when init tls_multi

When openvpn run in UDP server mode, if ssl connections reach the
max clients, the next connection would be failed in `multi_create_instance`
and the half connection will be close in `multi_close_instance`, which
may lead array `m->instances[0]` covered unexpectedly and make the
first connection interrupt, this patch fix this problem by init `peer_id`
with `MAX_PEER_ID` in `tils_multi_init`.

Signed-off-by: yatta <ytzhang01@foxmail.com
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <tencent_C49D67EAA5678D180C293706A9469EFE8307@qq.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg27260.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 3e30504d86f0fe5556acc0cb8e6975c5b2277661)