GATT: fix 32 bit UUID handling

When writing UUID into stream with gatt_build_uuid_to_stream, we always
use 16bit or 128bit representation. In GATT code returning service UUID,
we were returning 32bit representation lenght, even though 128bit
representation was being returned in the stream. This resulted in
invalid GATT database content being returned, and the service not being
visible.

Bug: 66912853
Test: create GATT database with 32bit UUID, discover from remote device
Change-Id: I791a518ab080bd99db0a8be18d97e865c838fc7e