Bluetooth: Support connection parameter update as central

bt_conn_le_param_update returns -EBUSY when used in central
role if peer did not support LE connection parameter
request.

This commit allows a central role to use either LE
connection parameter request, if local controller supports
it, else use LE connection update.

Jira: ZEP-1773

Change-id: I72b9c77440459672fd50216a74ffcbd59c5f38f6
Signed-off-by: Vinayak Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>