Bluetooth: hci_core: Fix not accounting for BIS/CIS/PA links separately

This fixes the likes of hci_conn_num(CIS_LINK) returning the total of
ISO connection which includes BIS_LINK as well, so this splits the
iso_num into each link type and introduces hci_iso_num that can be used
in places where the total number of ISO connection still needs to be
used.

Fixes: 23205562 ("Bluetooth: separate CIS_LINK and BIS_LINK link types")
Fixes: a7bcffc6 ("Bluetooth: Add PA_LINK to distinguish BIG sync and PA sync connections")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>