cli-command: unload modules synchronously

cli-command: unload modules synchronously

Users may want to change the parameters of some load-once modules in
~/.config/pulse/default.pa. That should be possible by including
/etc/pulse/default.pa from the per-user configuration file, and then
unloading a module and reloading it with different parameters. However,
that doesn't work, because the unload-module command will not unload the
module immediately, so the subsequent load-module command will fail when
the module can be loaded only once.

This patch makes the module unloading synchronous. "pacmd unload-module
module-cli-protocol-unix" is something that might not like this change,
since the command will unload the code that is processing the command,
but I tested it and it works fine. When pa_module_unload() is called,
that won't yet remove the module code from memory, the lt_dlclose() call
is postponed until it's safe to remove the code from memory.

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=102205