MEDIUM: quic: Dynamic allocations of QUIC TLS encryption levels

MEDIUM: quic: Dynamic allocations of QUIC TLS encryption levels

Replace ->els static array of encryption levels by 4 pointers into the QUIC
connection object, quic_conn struct.
    ->iel denotes the Initial encryption level,
    ->eel the Early-Data encryption level,
    ->hel the Handshaske encryption level and
    ->ael the Application Data encryption level.

Add ->qel_list to this structure to list the encryption levels after having been
allocated. Modify consequently the encryption level object itself (quic_enc_level
struct) so that it might be added to ->qel_list QUIC connection list of
encryption levels.

Implement qc_enc_level_alloc() to initialize the value of a pointer to an encryption
level object. It is used to initialized the pointer newly added to the quic_conn
structure. It also takes a packet number space pointer address as argument to
initialize it if not already initialized.

Modify quic_tls_ctx_reset() to call it from quic_conn_enc_level_init() which is
called by qc_enc_level_alloc() to allocate an encryption level object.

Implement 2 new helper functions:
  - ssl_to_qel_addr() to match and pointer address to a quic_encryption level
    attached to a quic_conn object with a TLS encryption level enum value;
  - qc_quic_enc_level() to match a pointer to a quic_encryption level attached
    to a quic_conn object with an internal encryption level enum value.
This functions are useful to be called from ->set_encryption_secrets() and
->add_handshake_data() TLS stack called which takes a TLS encryption enum
as argument (enum ssl_encryption_level_t).

Replace all the use of the qc->els[] array element values by one of the newly
added ->[ieha]el quic_conn struct member values.