MINOR: mworker/cli: create master CLI sockpair before fork

MINOR: mworker/cli: create master CLI sockpair before fork

The main idea here is to create a master CLI inherited sockpair just before the
master-worker fork. And only then after the fork let each process to bind a
needed listener to the its end of this sockpair.

Like this master and worker processes can close unused "ends" of its sockpair
copy (ipc_fd[0] for worker and and ipc_fd[1] for master).

When this sockpair creation happens inside the
mworker_cli_global_proxy_new_listener() is not possible for the master to
close ipc_fd[1] bound to the GLOBAL proxy listener, as this triggers a
BUG_ON(fd->owner) in fd_insert() in master context, because master process
has alredy entered in its polling loop and poller in its turn tries to reused
closed fd.