wifi: cfg80211: wext: fix IGTK key ID off-by-one

wifi: cfg80211: wext: fix IGTK key ID off-by-one

[ Upstream commit c8d7f21ead727485ebf965e2b4d42d4a4f0840f6 ]

The IGTK key ID must be 4 or 5, but the code checks against
key ID + 1, so must check against 5/6 rather than 4/5. Fix
that.

Reported-by: Jouni Malinen <j@w1.fi>
Fixes: 08645126dd24 ("cfg80211: implement wext key handling")
Link: https://patch.msgid.link/20260209181220.362205-2-johannes@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>