Transceiver unregister

Please never use `for (...);`, this only invites errors. Use `{}` instead, or better yet, refactor this code.
```c
for (i = 0; i < TRANSCEIVER_MAX_REGISTERED; ++i) {
    if ((reg[i].pid == pid) && (reg[i].transceivers != TRANSCEIVER_NONE)) {
        reg[i].transceivers &= ~t;
        return 1;
    }
}
return 0;
```