Drop the ternary operator for calculating ssid display length in list_scan().
Regardless if a verbose scan is required or not, we'd still want to display the
full SSID name by default so use the IEE80211_NWID_LEN constant to set the
value to use instead.

Tested on rene@'s laptop.
Reviewed by: kp
Sponsored by: Essen Hackathon
Differential Revision: https://reviews.freebsd.org/D16566