BUG/MEDIUM: stick-tables: fix ref counter in table entry using multiple http tracksc.

BUG/MEDIUM: stick-tables: fix ref counter in table entry using multiple http tracksc.

Setting multiple http-request track-scX rules generates entries
which never expires.

If there was already an entry registered by a previous http rule
'stream_track_stkctr(&s->stkctr[rule->action], t, ts)' didn't
register the new 'ts' into the stkctr. And function is left
with no reference on 'ts' whereas refcount had been increased
by the '_get_entry'

The patch applies the same policy as the one showed on tcp track
rules and if there is successive rules the track counter keep the
first entry registered in the counter and nothing more is computed.

After validation this should be backported in all versions.