Fix node registration ip on dual stack

[logan2211]

When using a user defined node ip on a dual stack cluster, k3s_node_ip will contain "ipv4,ipv6" IP. In order to properly set the registration IP, the first (preferred) IP in the list is used, and if it is the IPv6 IP it will be URL wrapped.

[logan2211]

FYI, tested 4 different ways:

• single stack, ipv4: k3s_node_ip set to "10.0.0.0"
• single stack, ipv6: k3s_node_ip set to "fdfc:0f9d:6133::2"
• dual stack, ipv4 preferred: k3s_node_ip = "10.0.0.0,fdfc:0f9d:6133::2"
• dual stack, ipv6 preferred: k3s_node_ip = "fdfc:0f9d:6133::2,10.0.0.0"

All work as expected.