【if_indextoname（unsigned ifindex, char *ifname）】if_indextoname（unsigned ifindex, char *ifname）
DESCRIPTION
The if_indextoname() function shall map an interface index to its corresponding name.
When this function is called, ifname shall point to a buffer of at least {IF_NAMESIZE} bytes. The function shall place in this buffer the name of the interface with index ifindex.
RETURN VALUE
If ifindex is an interface index, then the function shall return the value supplied in ifname, which points to a buffer now containing the interface name. Otherwise, the function shall
return a NULL pointer and set errno to indicate the error.
ERRORS
The if_indextoname() function shall fail if:
ENXIO The interface does not exist.
