slirp4netns: add builtin DNS server to resolv.conf

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

libpod/container_internal_linux.go

@@ -835,6 +835,10 @@ func (c *Container) generateResolvConf() (string, error) {
 
 	// Make a new resolv.conf
 	nameservers := resolvconf.GetNameservers(resolv.Content)
+	// slirp4netns has a built in DNS server.
+	if c.config.NetMode.IsSlirp4netns() {
+		nameservers = append(nameservers, "10.0.2.3")
+	}
 	if len(c.config.DNSServer) > 0 {
 		// We store DNS servers as net.IP, so need to convert to string
 		nameservers = []string{}