wl1251: specify max. IE length

This fix is similar to commit 77c91295

 ("wil6210: specify max. IE
length").  Without the max IE length set, wpa_supplicant cannot operate
using the nl80211 interface.

This patch is a workaround - the number 512 is taken from the wlcore
driver, but note that per Paul Fertser:

    there's no correct number because the driver will ignore the data
    passed in extra IEs.

Suggested-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Merlijn Wajer <merlijn@wizzup.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211212221310.5453-1-merlijn@wizzup.org