BUG/MINOR: quic: Wrong use of now_ms timestamps (cubic algo)

BUG/MINOR: quic: Wrong use of now_ms timestamps (cubic algo)

As now_ms may wrap, one must use the ticks API to protect the cubic congestion
control algorithm implementation from side effects due to this.

Furthermore to make the cubic congestion control algorithm more readable and easy
to maintain, adding a new state ("in recovery period" QUIC_CC_ST_RP new enum) helps
in reaching this goal. Implement quic_cc_cubic_rp_cb() which is the callback for
this new state.

Must be backported to 2.7 and 2.6.