Fix test_hotspot_upstream_cellular failure

This change:
  1. Move precondition checks prior to setup hotspot.
     This removes the need of redundant clean-up if
     the device doesn't meet preconditions.
  2. Use unregisterAll instead of unregisterCell to
     clean-up registered connections to prevent from
     complex error handling in clean-up stage.

Test: m connectivity_multi_devices_snippet && \
      atest CtsConnectivityMultiDevicesTestCases:ConnectivityMultiDevicesTest
Fix: 345110845
Change-Id: I4de0e7401d52f891948eb7b5a8c112a837cb0c3e
diff --git a/tests/cts/multidevices/snippet/ConnectivityMultiDevicesSnippet.kt b/tests/cts/multidevices/snippet/ConnectivityMultiDevicesSnippet.kt
index 8805edd..f4ad2c4 100644
--- a/tests/cts/multidevices/snippet/ConnectivityMultiDevicesSnippet.kt
+++ b/tests/cts/multidevices/snippet/ConnectivityMultiDevicesSnippet.kt
@@ -77,9 +77,9 @@
         ctsNetUtils.expectNetworkIsSystemDefault(network)
     }
 
-    @Rpc(description = "Unrequest cellular connection.")
-    fun unrequestCellular() {
-        cbHelper.unrequestCell()
+    @Rpc(description = "Unregister all connections.")
+    fun unregisterAll() {
+        cbHelper.unregisterAll()
     }
 
     @Rpc(description = "Ensure any wifi is connected and is the default network.")