MINOR: quic: RETIRE_CONNECTION_ID frame handling (RX)

MINOR: quic: RETIRE_CONNECTION_ID frame handling (RX)

Add ->curr_cid_seq_num new quic_conn struct frame to store the connection
ID sequence number currently used by the connection.
Implement qc_handle_retire_connection_id_frm() to handle this RX frame.
Implement qc_retire_connection_seq_num() to remove a connection ID from its
sequence number.
Implement qc_build_new_connection_id_frm to allocate a new NEW_CONNECTION_ID
frame from a CID.
Modify qc_parse_pkt_frms() which parses the frames of an RX packet to handle
the case of the RETIRE_CONNECTION_ID frame.

Must be backported to 2.7.