[geo] Extend DeviceAdmin unobtrusively with monkey patching

Prepend DeviceLocationInline to DeviceAdmin with monkey patching.
This allows to have other modules extending DeviceAdmin without
fighting each other.

openwisp_controller/geo/admin.py

@@ -6,9 +6,7 @@
 from openwisp_utils.admin import MultitenantOrgFilter
 
 from ..admin import MultitenantAdminMixin
-from ..config.admin import ConfigInline
-from ..config.admin import DeviceAdmin as BaseDeviceAdmin
-from ..config.models import Device
+from ..config.admin import DeviceAdmin
 from .models import DeviceLocation, FloorPlan, Location
 
 
@@ -71,11 +69,5 @@ class DeviceLocationInline(ObjectLocationMixin, admin.StackedInline):
 admin.site.register(Location, LocationAdmin)
 
 
-# Add DeviceLocationInline to config.DeviceAdmin
-
-class GeoDeviceAdmin(BaseDeviceAdmin):
-    inlines = [DeviceLocationInline, ConfigInline]
-
-
-admin.site.unregister(Device)
-admin.site.register(Device, GeoDeviceAdmin)
+# Prepend DeviceLocationInline to config.DeviceAdmin
+DeviceAdmin.inlines.insert(0, DeviceLocationInline)