socket-server: Move systemd socket activation code to pulsecore

There is no need to support server sockets in client library. Move all related
code and tcp-wrappers dependency to pulsecore library.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/640>

src/pulsecore/socket-server.c

@@ -642,3 +642,83 @@ char *pa_socket_server_get_address(pa_socket_server *s, char *c, size_t l) {
             return NULL;
     }
 }
+
+#ifdef HAVE_SYS_UN_H
+
+int pa_unix_socket_is_stale(const char *fn) {
+    struct sockaddr_un sa;
+    int fd = -1, ret = -1;
+
+    pa_assert(fn);
+
+    if ((fd = pa_socket_cloexec(PF_UNIX, SOCK_STREAM, 0)) < 0) {
+        pa_log("socket(): %s", pa_cstrerror(errno));
+        goto finish;
+    }
+
+    sa.sun_family = AF_UNIX;
+    strncpy(sa.sun_path, fn, sizeof(sa.sun_path)-1);
+    sa.sun_path[sizeof(sa.sun_path) - 1] = 0;
+
+    if (connect(fd, (struct sockaddr*) &sa, sizeof(sa)) < 0) {
+#if !defined(OS_IS_WIN32)
+        if (errno == ECONNREFUSED)
+            ret = 1;
+#else
+        if (WSAGetLastError() == WSAECONNREFUSED || WSAGetLastError() == WSAEINVAL)
+            ret = 1;
+#endif
+    } else
+        ret = 0;
+
+finish:
+    if (fd >= 0)
+        pa_close(fd);
+
+    return ret;
+}
+
+int pa_unix_socket_remove_stale(const char *fn) {
+    int r;
+
+    pa_assert(fn);
+
+#ifdef HAVE_SYSTEMD_DAEMON
+    {
+        int n = sd_listen_fds(0);
+        if (n > 0) {
+            for (int i = 0; i < n; ++i) {
+                if (sd_is_socket_unix(SD_LISTEN_FDS_START + i, SOCK_STREAM, 1, fn, 0) > 0) {
+                    /* This is a socket activated socket, therefore do not consider
+                    * it stale. */
+                    return 0;
+                }
+            }
+        }
+    }
+#endif
+
+    if ((r = pa_unix_socket_is_stale(fn)) < 0)
+        return errno != ENOENT ? -1 : 0;
+
+    if (!r)
+        return 0;
+
+    /* Yes, here is a race condition. But who cares? */
+    if (unlink(fn) < 0)
+        return -1;
+
+    return 0;
+}
+
+#else /* HAVE_SYS_UN_H */
+
+int pa_unix_socket_is_stale(const char *fn) {
+    return -1;
+}
+
+int pa_unix_socket_remove_stale(const char *fn) {
+    return -1;
+}
+
+#endif /* HAVE_SYS_UN_H */