Allow dynamic IP configuration for NEPacketTunnelNetworkSettings instead of hardcoded values

[Kerim-hash]

Currently, in PacketTunnelProvider.m the IP configuration is hardcoded:

`NEPacketTunnelNetworkSettings *networkSettings =
[[NEPacketTunnelNetworkSettings alloc]
initWithTunnelRemoteAddress:@"10.0.0.3"];

// IP address configuration
networkSettings.IPv4Settings = [[NEIPv4Settings alloc]
initWithAddresses:@[@"10.0.0.2"] subnetMasks:@[@"255.255.255.0"]];
`

Here, the remote address (10.0.0.3) and local address (10.0.0.2) are fixed values.
This makes the tunnel less flexible, since it cannot adapt to different server configurations.