Fix ALSA latency (causing ALSA not to block).

With arbitrarily large latency setting (unsigned int)-1, ALSA will happily
accept all the samples we want to throw at it.

Reducing to a reasonably long (but still sub-second) value of 100ms, we
cause ALSA writes to block and work properly with --tx-carrier.

src/simpleaudio-alsa.c

@@ -155,7 +155,7 @@ sa_alsa_open_stream(
 		channels,
 		rate,
 		1 /* soft_resample (allow) */,
-		(unsigned int)-1 /* latency (allow max to avoid underruns) */);
+		100000 /* latency (us) */);
     if (error) {
 	fprintf(stderr, "E: %s\n", snd_strerror(error));
 	snd_pcm_close(pcm);