hostap: Fix interface name copy in removal

Using a macro here that can potentially limit the interface name
compared to add can lead to issues, so, to mimic what we do in add, use
the sizeof with a boundary check.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>