Delay isc__nm_uvreq_t deallocation to connection callback

When the TCP, TCPDNS or TLSDNS connection times out, the isc__nm_uvreq_t would be pushed into sock->inactivereqs before the uv_tcp_connect() callback finishes. Because the isc__nmsocket_t keeps the list of inactive isc__nm_uvreq_t, this would cause use-after-free only when the sock->inactivereqs is full (which could never happen because the failure happens in connection timeout callback) or when the sock->inactivereqs mechanism is completely removed (f.e. when running under Address or Thread Sanitizer).

Delay isc__nm_uvreq_t deallocation to the connection callback and only signal the connection callback should be called by shutting down the libuv socket from the connection timeout callback.

(cherry picked from commit 32686279)

Closes #3166 (closed)