minor fixes for x2 + modify conf files

The configuration file has now to contain ENB_IPV4_ADDRESS_FOR_X2C and
ENB_PORT_FOR_X2C in the NETWORK_INTERFACES section.

For example:

    NETWORK_INTERFACES :
    {
        ENB_INTERFACE_NAME_FOR_S1_MME            = "eth0";
        ENB_IPV4_ADDRESS_FOR_S1_MME              = "192.168.12.111/24";
        ENB_INTERFACE_NAME_FOR_S1U               = "eth0";
        ENB_IPV4_ADDRESS_FOR_S1U                 = "192.168.12.111/24";
        ENB_PORT_FOR_S1U                         = 2152; # Spec 2152

        ENB_IPV4_ADDRESS_FOR_X2C                 = "192.168.12.111/24";
        ENB_PORT_FOR_X2C                         = 36422; # Spec 36422
    };