Revert "gatt: Remove reduntant `in_use` flag"

Revert submission 2268950

Bug: 257046947
Bug: 249431973
Test: reverting changes that broke earlier build
Reason for revert: b/257046947 infinite loop
Reverted Changes:
If19de77a8:gatt: Improve queueing of GATT messages
I1bfb4c546:gatt: Remove reduntant `in_use` flag
I1d3351ebc:gatt: Improve send queued request from tGATT_TCB

Change-Id: Ief553d755b4002030a4ae99e16d9f5ebba325235