Restore pre-NCP cipher options on SIGUSR1

Restore pre-NCP cipher options on SIGUSR1

As reported by debbie10t on the openvpn-devel list (Message-ID:
<326b8ff7-39a6-1974-c0b0-82fd2abdc7b7@gmail.com>), an NCP client will
attempt to reconnect with the previously pushed cipher, instead of the
cipher from the config file, after a sigusr1 restart.  This can be a
problem when the server is reconfigured (as debbie10t explainted), or when
roaming to a differently-configured server.  Fix this by restoring the
cipher options from the config file after a sigusr1 restart.

This makes the cipher options behaviour different from other pushable
options, because those are also cached until a sighup restart.  We might
want to change this behaviour in general, but for now let's just fix the
issue at hand.

v2: also cache and restore keysize, as that parameter is relevant too.
v3: inherit cached cipher options from parent context.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1478027207-28651-1-git-send-email-steffan@karger.me>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg12869.html
Signed-off-by: David Sommerseth <davids@openvpn.net>