MINOR: mux-h2/glitches: add a description to the H2 glitches

MINOR: mux-h2/glitches: add a description to the H2 glitches

Since we can now list them using "debug counters" and now support a
description, better add the description to all glitches. This patch may
be backported to 3.1, but before this the following patches must also
be picked:

    86823c828 MINOR: mux-h2/traces: add a missing trace on negative initial window size
    7c8e9420a CLEANUP: mux-h2/traces: reword certain ambiguous traces

(cherry picked from commit f0eca8fe73b5ddfbb642d39bdb8c4d67c200575b)
Signed-off-by: Willy Tarreau <w@1wt.eu>