[Web] Implement dummy IPWeb instead of IPUnix

Note: This commit ties the IPUnix to the UNIX_SOCKET_UNAVAILABLE define,
disabling it when set. It is maybe not semantically correct (getifaddrs)
is not part of the "socket" API, but it's reasonable to expect that a
platform not supporting Unix-style sockets, would also not support other
Unix network functions.

drivers/unix/os_unix.cpp

@@ -169,8 +169,8 @@ void OS_Unix::initialize_core() {
 
 #ifndef UNIX_SOCKET_UNAVAILABLE
 	NetSocketUnix::make_default();
-#endif
 	IPUnix::make_default();
+#endif
 	process_map = memnew((HashMap<ProcessID, ProcessInfo>));
 
 	_setup_clock();