Define a new field in listener structure named flags.
For the moment, no flag is defined. This will be notably useful to
differentiate QUIC listeners with the implementation of a QUIC conn
accept queue.
short int nice; /* nice value to assign to the instantiated tasks */
int luid; /* listener universally unique ID, used for SNMP */
int options; /* socket options : LI_O_* */
+ int flags; /* LI_F_* flags */
__decl_thread(HA_SPINLOCK_T lock);
struct fe_counters *counters; /* statistics counters */