Minor improvements in LE Create Connection handling

1. According to spec, controller should never send "Command Complete" event
after "LE Create Connection" or "LE Extened Create Connection" command.
Add error message in such case.

2. Parse Comand Status for LE Enhanced Create Connection.

3. Fix NPE in btm_ble_update_mode_operation, when called from
btm_ble_create_ll_conn_complete.

Test: Bond/unbond with few LE devices while connected.
Change-Id: Ic135d9a8d096634afe33997afb42d054237598c2