net: ieee802154: adf7242: Fix erroneous RX enable

[ Upstream commit 36d26d6b ]

Only enable RX mode if the netdev is opened.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>