examples: network-scan: enable modem before the network scan

Otherwise we get the following exception:

Traceback (most recent call last):
  File "/root/network-scan-python", line 57, in <module>
    networks = modem3gpp.scan_sync()
gi.repository.GLib.Error: mm_core_error_quark: GDBus.Error:org.freedesktop.ModemManager1.Error.Core.WrongState: Cannot scan networks: not enabled yet (8)

examples/network-scan-python/network-scan-python

@@ -19,6 +19,7 @@
 #
 
 import sys
+import time
 
 import gi
 gi.require_version('ModemManager', '1.0')
@@ -43,6 +44,9 @@ if __name__ == "__main__":
 
     # Iterate modems and scan network with each one by one
     for obj in manager.get_objects():
+        modem = obj.get_modem()
+        modem.enable()
+        time.sleep(1)
         modem3gpp = obj.get_modem_3gpp()
         if not modem3gpp:
             sys.stderr.write('%s: skipping unusable modem...\n' %