Move common code from Discover all Characteristics to GATT library

The attribute client (attrib/client.c) and gatttool share similar code
to parse the PDU coming from server. This commit moves this common code
to attrib/gatt.c, and simplifies the callbacks implemented by the
clients. The client callbacks are now called just once and get a GSList
of characteristics, instead of the raw PDU.
5 files changed