What is the number between brackets next to the interface name in ifconfig output?
In the following output i.e. (17)

en0 (17):
  inet address  192.168.4.5

What is the number between brackets next to the interface name in ifconfig output?
In the following output i.e. (17)

en0 (17):
  inet address  192.168.4.5

EDIT
As requested I add more info.
I was using ifconfig on Ventura but this called the Homebrew command instead the native one.
Using /sbin/ifconfig i got the output without the brackets.

en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
...
..