dns: show the last lookup with the servers

The answer to a lookup arrives after the command has returned, so the
console of the web interface never shows it. Plain "dns" now prints the
name and the address, or whether it is still pending or failed.

dns.c

@@ -200,6 +200,18 @@ void dns_show(void) __banked
 	print_string(", from DHCP ");
 	print_ip(dhcp_state.dns);
 	write_char('\n');
+	if (!dns_state.name[0])
+		return;
+	print_string("Last lookup ");
+	print_string_x(dns_state.name);
+	print_string(": ");
+	if (dns_state.status == DNS_DONE)
+		print_ip(dns_state.addr);
+	else if (dns_state.status == DNS_PENDING)
+		print_string("pending");
+	else
+		print_string("failed");
+	write_char('\n');
 }