BUG/MINOR: mux-quic: free task on qc_init() app ops failure

BUG/MINOR: mux-quic: free task on qc_init() app ops failure

qc_init() is used to initialize a QUIC MUX instance. On failure, each
resources are released via a series of goto statements. There is one
issue if the app_ops.init callback fails. In this case, MUX task is not
freed.

This can cause a crash as the task is already scheduled. When the
handler will run, it will crash when trying to access qcc instance.

To fix this, properly destroy qcc task on fail_install_app_ops label.

The impact of this bug is minor as app_ops.init callback succeeds most
of the time. However, it may fail on allocation failure due to memory
exhaustion.

This may fix github issue #2154.

This must be backported up to 2.7.