Bluetooth: Move buffer handling into a dedicated file

The buffer handling code is quite large and will continue to grow. As
it's not strictly HCI core material it's better to just manage it in a
separate file. This patch moves the code to include/bluetooth/buf.h
and net/bluetooth/buf.c.

Change-Id: Ie1ff79ac2cfa132359ce9f7674ff812d34b228aa
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
4 files changed