openconnect: set config variable on teardown and correctly pass the password

This addresses https://dev.openwrt.org/ticket/16634

Signed-off-by: Nikos Mavrogiannopoulos <nmav@gnutls.org>
openconnect: openconnect-wrapper would trap signals and send the correct one to server

Signed-off-by: Nikos Mavrogiannopoulos <nmav@gnutls.org>