Get statistics data from PGEN-descriptor

[slankdev]

We want a function that gets statistical-data from PGEN-descriptor.

[slankdev]

Implementation example)

   pgen_t* handle = pgen_open_offline("in.pcapng", PCAPNG_READ);
    if(handle == NULL){
        pgen_perror("oopes");
        return -1;
    }
    struct pgen_statistics ps;
    u_char buf[1000];
    int buflen;
    while(1){
        buflen = pgen_recvpacket_handle(handle, buf, buflen);
        if(buflen < 0){
            pgen_perror("oops");
            break;
        }else if(buflen == 0){
            break;
        }
    }
    pgen_getstatistic(handle, &ps);
    pgen_close(handle);

I'm going to implement new function that gets statistical data. However, I didn't decide function specification. 1st, I have to decide one.