CLI "show quic" output can be filtered to only a single connection entry
by specifying its address as argument. However, loop iteration and
filtering was incorrectly implemented, and in effect only the first
connection of each thread could be dumped this way.
Fix this by adjusting iteration on "show quic" handler. The basic idea
is similar. If <ctx.ptr> is set, it does not dump anything for
non-matching entries. As soon as the filtered entry is dumped, the
iteration is interrupted.