VirtualGatewayFactory getGatewayFactory() {
        // Make sure the virtual gateway not be null.
        return mNetBareConfig.gatewayFactory == null ? DefaultVirtualGatewayFactory.create() :
                mNetBareConfig.gatewayFactory;
    }
Remove a previously installed service state callback.

@param listener The callback to remove.
netbare-core/src/main/java/com/github/megatronking/netbare/NetBare.java