Bluetooth: Fix missing LE conn param req bit in set LE evt mask

With the introduction of event mask implementation in the
Controller, it is discovered that peer centrals
initiating LE connection parameter requests timed out as
the Host did not get/enable the HCI LE connection parameter
request event in the set LE event mask command.

Fix by adding the LE connection parameter request event bit
mask while creating set LE event mask command.

Jira: ZEP-2027

Change-id: Ida7750f375addc8a91036fffc47325518a3d2ec0
Signed-off-by: Vinayak Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>