net: convert standalone SetSocketNonBlocking() to Sock::SetNonBlocking()

This further encapsulates syscalls inside the `Sock` class.

Co-authored-by: practicalswift <practicalswift@users.noreply.github.com>

src/test/fuzz/util.cpp

@@ -254,6 +254,19 @@ int FuzzedSock::GetSockName(sockaddr* name, socklen_t* name_len) const
     return 0;
 }
 
+bool FuzzedSock::SetNonBlocking() const
+{
+    constexpr std::array setnonblocking_errnos{
+        EBADF,
+        EPERM,
+    };
+    if (m_fuzzed_data_provider.ConsumeBool()) {
+        SetFuzzedErrNo(m_fuzzed_data_provider, setnonblocking_errnos);
+        return false;
+    }
+    return true;
+}
+
 bool FuzzedSock::IsSelectable() const
 {
     return m_selectable;