Merge branch 'bugfix/btdm_add_some_comment' into 'master'

Component/bt: add some comments

See merge request idf/esp-idf!1949

diff --cc components/bt/bluedroid/bta/gatt/bta_gattc_api.c
Simple merge

diff --cc examples/bluetooth/blufi/main/blufi_example_main.c
Simple merge

diff --cc examples/bluetooth/gatt_security_client/main/example_ble_sec_gattc_demo.c
Simple merge

diff --cc examples/bluetooth/gatt_security_server/main/example_ble_sec_gatts_demo.c
Simple merge

diff --cc examples/bluetooth/gatt_server_service_table/main/gatts_table_creat_demo.c
Simple merge