test: also reset CConnman::m_private_broadcast in tests

Member variables of `CConnman::m_private_broadcast` (introduced in
https://github.com/bitcoin/bitcoin/pull/29415) could influence the tests
which creates non-determinism if the same instance of `CConnman` is used
for repeated test iterations.

So, reset the state of `CConnman::m_private_broadcast` from
`ConnmanTestMsg::Reset()`. Currently this affects the fuzz tests
`process_message` and `process_messages`.

Reported in
https://github.com/bitcoin/bitcoin/issues/34476#issuecomment-3849088794

src/net.h

@@ -1241,7 +1241,7 @@ public:
         /// Wait for the number of needed connections to become greater than 0.
         void NumToOpenWait() const;
 
-    private:
+    protected:
         /**
          * Check if private broadcast can be done to IPv4 or IPv6 peers and if so via which proxy.
          * If private broadcast connections should not be opened to IPv4 or IPv6, then this will
@@ -1251,6 +1251,8 @@ public:
 
         /// Number of `ConnectionType::PRIVATE_BROADCAST` connections to open.
         std::atomic_size_t m_num_to_open{0};
+
+        friend struct ConnmanTestMsg;
     } m_private_broadcast;
 
     bool CheckIncomingNonce(uint64_t nonce);

src/test/util/net.cpp

@@ -84,6 +84,8 @@ void ConnmanTestMsg::Reset()
 {
     ResetAddrCache();
     ResetMaxOutboundCycle();
+    m_private_broadcast.m_outbound_tor_ok_at_least_once.store(false);
+    m_private_broadcast.m_num_to_open.store(0);
 }
 
 void ConnmanTestMsg::NodeReceiveMsgBytes(CNode& node, std::span<const uint8_t> msg_bytes, bool& complete) const