gatt-database: No multiple calls to AcquireWrite

gatt-database: No multiple calls to AcquireWrite

This checks if an outstanding call to AcquireWrite is already in
progress. If so, the write request is placed into the queue, but
AcquireWrite is not called again. When a response to AcquireWrite is
received, acquire_write_reply sends all queued writes over the acquired
socket.

Making multiple simultaneous calls to AcquireWrite makes no sense,
as this would open multiple socket pairs and only the last returned
socket would be used for further writes.

Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>