Merge bitcoin/bitcoin#21879: refactor: wrap accept() and extend usage of Sock

6bf6e9fd9d net: change CreateNodeFromAcceptedSocket() to take Sock (Vasil Dimov)
9e3cbfca7c net: use Sock in CConnman::ListenSocket (Vasil Dimov)
f8bd13f85a net: add new method Sock::Accept() that wraps accept() (Vasil Dimov)

Pull request description:

  _This is a piece of https://github.com/bitcoin/bitcoin/pull/21878, chopped off to ease review._

  Introduce an `accept(2)` wrapper `Sock::Accept()` and extend the usage of `Sock` in `CConnman::ListenSocket` and `CreateNodeFromAcceptedSocket()`.

ACKs for top commit:
  laanwj:
    Code review ACK 6bf6e9fd9d
  jamesob:
    ACK 6bf6e9fd9d ([`jamesob/ackr/21879.2.vasild.wrap_accept_and_extend_u`](https://github.com/jamesob/bitcoin/tree/ackr/21879.2.vasild.wrap_accept_and_extend_u))
  jonatack:
    ACK 6bf6e9fd9d per `git range-diff ea989de 976f6e8 6bf6e9f` -- only change since my last review was `s/listen_socket.socket/listen_socket.sock->Get()/` in `src/net.cpp: CConnman::SocketHandlerListening()` -- re-read the code changes, rebase/debug build/ran units following my previous full review (https://github.com/bitcoin/bitcoin/pull/21879#pullrequestreview-761251278)
  w0xlt:
    tACK 6bf6e9f

Tree-SHA512: dc6d1acc4f255f1f7e8cf6dd74e97975cf3d5959e9fc2e689f74812ac3526d5ee8b6a32eca605925d10a4f7b6ff1ce5e900344311e587d19786b48c54d021b64

src/test/fuzz/util.cpp

@@ -13,6 +13,8 @@
 #include <util/time.h>
 #include <version.h>
 
+#include <memory>
+
 FuzzedSock::FuzzedSock(FuzzedDataProvider& fuzzed_data_provider)
     : m_fuzzed_data_provider{fuzzed_data_provider}
 {
@@ -158,6 +160,20 @@ int FuzzedSock::Connect(const sockaddr*, socklen_t) const
     return 0;
 }
 
+std::unique_ptr<Sock> FuzzedSock::Accept(sockaddr* addr, socklen_t* addr_len) const
+{
+    constexpr std::array accept_errnos{
+        ECONNABORTED,
+        EINTR,
+        ENOMEM,
+    };
+    if (m_fuzzed_data_provider.ConsumeBool()) {
+        SetFuzzedErrNo(m_fuzzed_data_provider, accept_errnos);
+        return std::unique_ptr<FuzzedSock>();
+    }
+    return std::make_unique<FuzzedSock>(m_fuzzed_data_provider);
+}
+
 int FuzzedSock::GetSockOpt(int level, int opt_name, void* opt_val, socklen_t* opt_len) const
 {
     constexpr std::array getsockopt_errnos{