podman: relay custom DNS servers to network stack

Aardvark-dns and netavark now accepts custom DNS servers for containers
via new config field `dns_servers`. New field allows containers to use
custom resolvers instead of host's default resolvers.

Following commit instruments libpod to pass these custom DNS servers set
via `--dns` or central config to the network stack.

Depends-on:
* Common: containers/common#1189
* Netavark: containers/netavark#452
* Aardvark-dns: containers/aardvark-dns#240

Signed-off-by: Aditya R <[email protected]>

libpod/networking_common.go

@@ -39,9 +39,15 @@ func (c *Container) convertPortMappings() []types.PortMapping {
 }
 
 func (c *Container) getNetworkOptions(networkOpts map[string]types.PerNetworkOptions) types.NetworkOptions {
+	nameservers := make([]string, 0, len(c.runtime.config.Containers.DNSServers)+len(c.config.DNSServer))
+	nameservers = append(nameservers, c.runtime.config.Containers.DNSServers...)
+	for _, ip := range c.config.DNSServer {
+		nameservers = append(nameservers, ip.String())
+	}
 	opts := types.NetworkOptions{
 		ContainerID:   c.config.ID,
 		ContainerName: getNetworkPodName(c),
+		DNSServers:    nameservers,
 	}
 	opts.PortMappings = c.convertPortMappings()