net: rename Sock::Reset() to Sock::Close() and make it private

Outside of `Sock`, `Sock::Reset()` was used in just one place (in
`i2p.cpp`) which can use the assignment operator instead.

This simplifies the public `Sock` API by having one method less.

src/test/fuzz/util.cpp

@@ -24,10 +24,10 @@ FuzzedSock::FuzzedSock(FuzzedDataProvider& fuzzed_data_provider)
 FuzzedSock::~FuzzedSock()
 {
     // Sock::~Sock() will be called after FuzzedSock::~FuzzedSock() and it will call
-    // Sock::Reset() (not FuzzedSock::Reset()!) which will call close(m_socket).
+    // close(m_socket) if m_socket is not INVALID_SOCKET.
     // Avoid closing an arbitrary file descriptor (m_socket is just a random very high number which
     // theoretically may concide with a real opened file descriptor).
-    Reset();
+    m_socket = INVALID_SOCKET;
 }
 
 FuzzedSock& FuzzedSock::operator=(Sock&& other)
@@ -36,11 +36,6 @@ FuzzedSock& FuzzedSock::operator=(Sock&& other)
     return *this;
 }
 
-void FuzzedSock::Reset()
-{
-    m_socket = INVALID_SOCKET;
-}
-
 ssize_t FuzzedSock::Send(const void* data, size_t len, int flags) const
 {
     constexpr std::array send_errnos{

src/test/fuzz/util.h

@@ -55,8 +55,6 @@ public:
 
     FuzzedSock& operator=(Sock&& other) override;
 
-    void Reset() override;
-
     ssize_t Send(const void* data, size_t len, int flags) const override;
 
     ssize_t Recv(void* buf, size_t len, int flags) const override;

src/test/sock_tests.cpp

@@ -69,14 +69,6 @@ BOOST_AUTO_TEST_CASE(move_assignment)
     BOOST_CHECK(SocketIsClosed(s));
 }
 
-BOOST_AUTO_TEST_CASE(reset)
-{
-    const SOCKET s = CreateSocket();
-    Sock sock(s);
-    sock.Reset();
-    BOOST_CHECK(SocketIsClosed(s));
-}
-
 #ifndef WIN32 // Windows does not have socketpair(2).
 
 static void CreateSocketPair(int s[2])

src/test/util/net.h

@@ -100,7 +100,7 @@ public:
         m_socket = INVALID_SOCKET - 1;
     }
 
-    ~StaticContentsSock() override { Reset(); }
+    ~StaticContentsSock() override { m_socket = INVALID_SOCKET; }
 
     StaticContentsSock& operator=(Sock&& other) override
     {
@@ -108,11 +108,6 @@ public:
         return *this;
     }
 
-    void Reset() override
-    {
-        m_socket = INVALID_SOCKET;
-    }
-
     ssize_t Send(const void*, size_t len, int) const override { return len; }
 
     ssize_t Recv(void* buf, size_t len, int flags) const override