Added the possibility to allow traffic from an additional IPv4 address/subnet

Previously only the IPv4 addresses reported by the Filedaemons were allowed to
contact the Storagedaemon. Sometimes this does not work, but the new
$allow_additional_ipv4_address parameter can defined to work around this issue.

Signed-off-by: Samuli Seppänen <samuli@openvpn.net>