Support for tunnel IPv6 addresses

[dme]

My tunnel provider ($DAYJOB) has started to supply IPv6 addresses for the tunnel. ocproxy should be able to configure the lwip IPv6 stack accordingly.

[ljluestc]

#include <stdio.h>
#include <string.h>
#include <lwip/netif.h>
#include <lwip/ip_addr.h>
#include <lwip/init.h>
#include <lwip/inet.h>

#define TUNNEL_IPV6_PREFIX "2001:db8::" 

void configure_ipv6_tunnel(const char* ipv6_address) {
    ip_addr_t ipv6_addr;

    
    if (ip6addr_aton(ipv6_address, &ipv6_addr)) {
        
        struct netif* netif = netif_default; 
        netif_set_ip6_addr(netif, 0, &ipv6_addr); 
        netif_set_up(netif); 
        printf("Configured IPv6 address: %s\n", ipv6_address);
    } else {
        printf("Invalid IPv6 address: %s\n", ipv6_address);
    }
}

int main() {
    lwip_init(); 

    
    const char* tunnel_ipv6_address = TUNNEL_IPV6_PREFIX "1"; 
    configure_ipv6_tunnel(tunnel_ipv6_address);

    

    return 0;
}