Merge "AAudio loopback example, remove gain" into main

    printf("      -C{channels}      number of input channels\n");

    printf("      -D{deviceId}      input device ID\n");

    printf("      -F{0,1,2}         input format, 1=I16, 2=FLOAT\n");

    printf("      -g{gain}          recirculating loopback gain\n");

    printf("      -h{hangMillis}    occasionally hang in the callback\n");

    printf("      -P{inPerf}        set input AAUDIO_PERFORMANCE_MODE*\n");

    printf("          n for _NONE\n");

    int                   written                    = 0;

    int                   testMode                   = TEST_LATENCY;

    double                gain                       = 1.0;

    int                   hangTimeMillis             = 0;

    std::string           report;

                    case 'F':

                        requestedInputFormat = atoi(&arg[2]);

                        break;

                    case 'g':

                        gain = atof(&arg[2]);

                        break;

                    case 'h':

                        // Was there a number after the "-h"?

                        if (arg[2]) {