BUG/MINOR: mux-h2: fix the "show fd" dest buffer for the subscriber

Commit 98e40b981 ("MINOR: mux-h2: make the "show fd" helper also decode
the h2s subscriber when known") improved the output of "show fd" for the
H2 mux, but the output is sent to the trash buffer instead of the msg
argument. It turns out that this has no effect right now as the caller
passes the trash but this is risky.

This should be backported to 2.4.
1 file changed