BUG/MINOR: quic: adjust quic_tls prototypes

BUG/MINOR: quic: adjust quic_tls prototypes

Two prototypes in quic_tls module were not identical to the actual
function definition.

* quic_tls_decrypt2() : the second argument const attribute is not
  present, to be able to use it with EVP_CIPHER_CTX_ctlr(). As a
  consequence of this change, token field of quic_rx_packet is now
  declared as non-const.

* quic_tls_generate_retry_integrity_tag() : the second argument type
  differ between the two. Adjust this by fixing it to as unsigned char
  to match EVP_EncryptUpdate() SSL function.

This situation did not seem to have any visible effect. However, this is
clearly an undefined behavior and should be treated as a bug.

This should be backported up to 2.6.