Stop leaking mutex in nmworker and cond in nm socket

Stop leaking mutex in nmworker and cond in nm socket

On FreeBSD, the pthread primitives are not solely allocated on stack,
but part of the object lives on the heap.  Missing pthread_*_destroy
causes the heap memory to grow and in case of fast lived object it's
possible to run out-of-memory.

Properly destroy the leaking mutex (worker->lock) and
the leaking condition (sock->cond).

(cherry picked from commit 57d0fabaddf0e7ac297a046b084df8fb22d54d51)