app_rpt: Channel initialization for PTT

app_rpt is not waiting long enough in rpt_setup_channels for chan_simpleusb to
initialize the usb device before asserting PTT on/off.

This change adds a 250ms delay before asserting PTT on and another 50ms delay
before asserting PTT off.

I believe the intention of the original code was to insure that the PTT was
toggled immediately after the channel driver was created by app_rpt.

Testing by the effected users is needed. This may close #421 and #424.

apps/app_rpt.c

@@ -2695,8 +2695,12 @@ static int rpt_setup_channels(struct rpt *myrpt, struct ast_format_cap *cap)
 		myrpt->txchannel = myrpt->rxchannel;
 		myrpt->dahditxchannel = IS_DAHDI_CHAN_NAME(myrpt->rxchanname) && !IS_PSEUDO_NAME(myrpt->rxchanname) ? myrpt->txchannel : NULL;
 	}
+	/* If the TX channel is not a pseudo channel, toggle the PTT line */
 	if (!IS_PSEUDO(myrpt->txchannel)) {
+		/* Wait for the driver to finish initialization */
+		usleep(250000);
 		ast_indicate(myrpt->txchannel, AST_CONTROL_RADIO_KEY);
+		usleep(50000);
 		ast_indicate(myrpt->txchannel, AST_CONTROL_RADIO_UNKEY);
 	}