chan_dahdi: Change 999999 to INT_MAX to better reflect "no timeout"

The no-entry timeout set to 999999 == 16⅔ minutes, change to INT_MAX
to match behavior of "no timeout" defined in comment.

ASTERISK-28702 #close

Change-Id: I4ea015986e061374385dba247b272f7aac60bf11

channels/chan_dahdi.c

@@ -9847,7 +9847,7 @@ static void *analog_ss_thread(void *data)
 		/* If starting a threeway call, never timeout on the first digit so someone
 		   can use flash-hook as a "hold" feature */
 		if (p->subs[SUB_THREEWAY].owner)
-			timeout = 999999;
+			timeout = INT_MAX;
 		while (len < AST_MAX_EXTENSION-1) {
 			int is_exten_parking = 0;