Only return early from BlockUntilSyncedToCurrentChain if current tip

is exact match

In the next commit, we start using BlockConnected/BlockDisconnected
callbacks to establish tx depth, rather than querying the chain
directly.

Currently, BlockUntilSyncedToCurrentChain will return early if
the best block processed by the wallet is a descendant of the node'tip.
That means that in the case of a re-org, it won't wait for the
BlockDisconnected callbacks that have been enqueued during the re-org
but have not yet been triggered in the wallet.

Change BlockUntilSyncedToCurrentChain to only return early if the
wallet's m_last_block_processed matches the tip exactly. This ensures
that there are no BlockDisconnected or BlockConnected callbacks
in-flight.

src/interfaces/chain.h

@@ -236,9 +236,8 @@ public:
     virtual std::unique_ptr<Handler> handleNotifications(Notifications& notifications) = 0;
 
     //! Wait for pending notifications to be processed unless block hash points to the current
-    //! chain tip, or to a possible descendant of the current chain tip that isn't currently
-    //! connected.
-    virtual void waitForNotificationsIfNewBlocksConnected(const uint256& old_tip) = 0;
+    //! chain tip.
+    virtual void waitForNotificationsIfTipChanged(const uint256& old_tip) = 0;
 
     //! Register handler for RPC. Command is not copied, so reference
     //! needs to remain valid until Handler is disconnected.