iw: Fix LICENSE

The contents of the COPYING file included in the source code match
those of ISC license:
https://git.kernel.org/pub/scm/linux/kernel/git/jberg/iw.git/tree/COPYING?h=v6.9
which seems to have been in effect since 2008 commit
https://git.kernel.org/pub/scm/linux/kernel/git/jberg/iw.git/commit?id=622c36ae94a880fb53f7f051f1b26616f5b553c1


("license under ISC").

(From OE-Core rev: 87da7445a2a77fe73e3524cd50112842e91235b6)

(From OE-Core rev: 686abc98421198d8224423cc95f97e3cd16296c1)

Signed-off-by: Niko Mauno <niko.mauno@vaisala.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Steve Sakoman <steve@sakoman.com>