MINOR: quic: simplify qc_parse_pkt_frms() return path

MINOR: quic: simplify qc_parse_pkt_frms() return path

Change qc_parse_pkt_frms() return path for normal and error cases. Most
notably, it allows to remove local variable ret as now return value is
hardcoded on normal and err label. This also allows to define a
different trace for error leaving code.

(cherry picked from commit 498a99a84956535a9ce2a61cb908d0fc81165606)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>