BUG/MINOR: mux-quic: fix wakeup on qcc_set_error()

BUG/MINOR: mux-quic: fix wakeup on qcc_set_error()

The following patch was a major refactoring of QUIC MUX. It removes
pacing specific code path. In particular, qcc_wakeup() utility function
was removed and replaced by its tasklet_wakup() usage.
  41f0472d967b2deb095d5adc8a167da973fbee3d
  MEDIUM: mux-quic: remove pacing specific code on qcc_io_cb

However, an incorrect substitution was performed in qcc_set_error(). As
such, there was no explicit wakeup in case an error is detected by QUIC
MUX or the app protocol layer. This may lead to missing error reporting
to clients.

Fix this by re-add tasklet_wakup() usage into qcc_set_error().

This must be backported up to 3.1 where above patch is scheduled.