Fix GATT discovery service fail over BR/EDR

According to the current gattc state machine, stack queues
discovery services request comes from framework when gattc
is in BTA_GATTC_DISCOVER_ST state. This request is re-scheduled
after discovery on server finished in bta_gattc_disc_cmpl
and return the discovery results to framemwork. But now, stack
assumed LE transport in code, which prevents discovery services
executing. This error can be detected by ACTS GATTOverBrEdrTest:
test_gatt_bredr_connect_trigger_on_services_discovered

Fix assumed transport to actual situantion

Test: ACTS GATTOverBrEdrTest:
test_gatt_bredr_connect_trigger_on_services_discovered
Change-Id: I110a0a3c19595fb76c3bb15b092ce18ebf7b11bf