BUG/MINOR: quic: ensure handshake speed up is only run once per conn

BUG/MINOR: quic: ensure handshake speed up is only run once per conn

When a duplicated CRYPTO frame is received during handshake, a server
may consider that there was a packet loss and immediately retransmit its
pending CRYPTO data without having to wait for PTO expiration. However,
RFC 9002 indicates that this should only be performed at most once per
connection to avoid excessive packet transmission.

QUIC connection is flagged with QUIC_FL_CONN_HANDSHAKE_SPEED_UP to mark
that a fast retransmit has been performed. However, during the
refactoring on CRYPTO handling with the storage conversion from ncbuf to
ncbmbuf, the check on the flag was accidentely removed. The faulty patch
is the following one :

  commit f50425c021eceb324add6873b58cc5f366554d31
  MINOR: quic: remove received CRYPTO temporary tree storage

This patch adds again the check on QUIC_FL_CONN_HANDSHAKE_SPEED_UP
before initiating fast retransmit. This ensures this is only performed
once per connection.

This must be backported up to 3.3.