The ifaddrlistx() function is similar to ifaddrlist(), but:

    * Allows specific address flags to be matched against.
    * Provides the addresses for a *specific* interface name
    *  a linked-list rather than an array so that information
      can grow over time without affecting binary compatibility.
    * Returns the number of items on the linked list on success,
      or -1 on failure.
    * Leaves error-handling up to the caller.

Specifically:

   int ifaddrlistx(const char *ifname, uint64_t set, uint64_t clear,
       ifaddrlistx_t **ifaddrp);

     * ifname: Interface name to match against.

     * set: One or more flags that must be set on the address for
       it to be returned.

     * clear: Flags that must be clear on the address for it to be
       returned.

     * ifaddrp: Upon success, ifaddrlistx() sets *ifaddrp to the head
       of a dynamically-allocated array of ifaddrlistx structures.  The
       ifaddrlistx structure is defined as:

       typedef struct ifaddrlistx {
		struct ifaddrlistx	*ia_next;
		char			ia_name[LIFNAMSIZ];
		uint64_t		ia_flags;
		struct sockaddr_storage	ia_addr;
       } ifaddrlistx_t;

Once done, the caller must free `ifaddrp' by calling ifaddrlistx_free():

   void ifaddrlistx_free(ifaddrlistx_t *ifaddrp);