discoverer: Fix a missing import

Change-Id: Iad485a2f4834aacf1d2e44519d796d0329810761
diff --git a/mdt/discoverer.py b/mdt/discoverer.py
index d09f665..b4664c6 100644
--- a/mdt/discoverer.py
+++ b/mdt/discoverer.py
@@ -1,6 +1,8 @@
 from typing import cast
 from zeroconf import ServiceBrowser, Zeroconf
 
+import socket
+
 class Discoverer:
     def __init__(self):
         self.zeroconf = Zeroconf()