drmgr: raise log rotation threshold

[nathanlynch]

The log rotation threshold is a mere 25000 bytes:

dr_fini(void)
{
    struct stat sbuf;
    int max_dr_log_sz = 25000;
...
    rc = stat(DR_LOG_PATH, &sbuf);
...
    if (sbuf.st_size >= max_dr_log_sz) {
        fprintf(stderr, "Rotating logs...\n");
...

Raising the rotation limit to something like 1MB would help problem determination by preserving more history and would better accommodate higher detail levels (e.g. -d 15 to get librtas debug output).

[tyreld]

Fixed by commit 88ebfd97d1c4