tcpsocket: add option to add server ip

A new config option allows to add a server ip
	option server_ip '10.0.0.2'

However, this server does not send anything back. Therefore it is not
possible to change the node configuration. This will probably be added
soon. The main goal of this commit is to allow monitoring of all nodes
in a network with DAWN, e.g. clients, channel utilization, ...

Also a network option (3) has been added which allows to use TCP but
not to announce your daemon in the broadcast domain. This allows you to
create a monitor-only node that holds only the local information and
forwards it to the central server.

A monitor-only node could be configured like
	option server_ip '10.0.0.1'
	option tcp_port '1026'
	option network_option '3'

Another possible config is
        option server_ip '10.0.0.1'
        option tcp_port '1026'
        option network_option '3'
Here, the node shares information with a central server, which can be
located outside the broadcast domain. Nevertheless, it also shares
information within its broadcast domain and can therefore perform
client steering.

src/include/datastorage.h

@@ -97,6 +97,7 @@ struct time_config_s {
 struct network_config_s {
     char broadcast_ip[MAX_IP_LENGTH];
     int broadcast_port;
+    char server_ip[MAX_IP_LENGTH];
     int tcp_port;
     int network_option;
     char shared_key[MAX_KEY_LENGTH];