Set capture buffer size

"-B buffer_size/--buffer-size=buffer_size" option can be used to change capture buffer size (code is here):

......
#if defined(HAVE_PCAP_CREATE) || defined(_WIN32)
        case 'B':
            Bflag = atoi(optarg)*1024;
            if (Bflag <= 0)
                error("invalid packet buffer size %s", optarg);
            break;
#endif /* defined(HAVE_PCAP_CREATE) || defined(_WIN32) */
......

The unit is KiB. pcap_set_buffer_size() is called to set buffer size (code is here):

......
if (Bflag != 0) {
    status = pcap_set_buffer_size(pc, Bflag);
    if (status != 0)
        error("%s: Can't set buffer size: %s",
            device, pcap_statustostr(status));
}
......

On Windows, a special processing is needed (code is here):

......
#if !defined(HAVE_PCAP_CREATE) && defined(_WIN32)
        if(Bflag != 0)
            if(pcap_setbuff(pd, Bflag)==-1){
                error("%s", pcap_geterr(pd));
            }
#endif /* !defined(HAVE_PCAP_CREATE) && defined(_WIN32) */
......