Bluetooth: use inclusive language in hci_core.h

This patch replaces some non-inclusive terms based on the appropriate
language mapping table compiled by the Bluetooth SIG:
https://specificationrefs.bluetooth.com/language-mapping/Appropriate_Language_Mapping_Table.pdf



Specifically, these terms are replaced:
master -> central
slave  -> peripheral

These attributes are not used elsewhere in the code.

Signed-off-by: Archie Pusaka <apusaka@chromium.org>
Reviewed-by: Miao-chen Chou <mcchou@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>