Clarify API doc for BluetoothGattServer::addService

Clarify that the caller has to wait for onServiceAdded callback before
calling BluetoothGattServer::addService again.

Bug: 72717069
Test: Compile
Change-Id: I20b031c724ba64bfd71cf10e58e587f69e4a2555
(cherry picked from commit 4b5cf4856064efbc018c0f2b4d6d3ff199403ee0)
1 file changed