shared/gatt-client: Add coexistence of long write and prepare write

This patch makes sure that long write is not proceeded when prepare
write has been called. Instead long write commands will be queued and
once write execute command is done, queued long write requests will
be proceeded.

It does not work in other way. Meaning, when long write is ongoing,
prepare write will not be proceeded nor queued. This feature can be
added later on if really needed.
1 file changed