net: move state dependent peer services flags

No behavior change. Just an intermediate refactoring.

By relocating the peer desirable services flags into the peer
manager, we allow the connections acceptance process to handle
post-IBD potential stalling scenarios.

In the follow-up commit(s), the desirable service flags will be
dynamically adjusted to detect post-IBD stalling scenarios (such
as a +48-hour inactive node that must prefer full node connections
instead of limited peer connections because they cannot provide
historical blocks). Additionally, this encapsulation enable us
to customize the connections decision-making process based on
new user's configurations in the future.

src/net.h

@@ -1005,6 +1005,12 @@ public:
     /** Handle removal of a peer (clear state) */
     virtual void FinalizeNode(const CNode& node) = 0;
 
+    /**
+     * Callback to determine whether the given set of service flags are sufficient
+     * for a peer to be "relevant".
+     */
+    virtual bool HasAllDesirableServiceFlags(ServiceFlags services) const = 0;
+
     /**
     * Process protocol messages received from a given node
     *