Bluetooth: making enable_hs independent from L2CAP

Fixes bluetooth compiling when CONFIG_BT_L2CAP is not enabled

net/built-in.o: In function `hci_dev_open':
(.text+0xdce9a): undefined reference to `enable_hs'

Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>