zmq: apply tx_gain to transmitted signal

This feature was temporary disabled in 497e183487

lib/src/phy/rf/rf_zmq_imp.c

@@ -961,8 +961,7 @@ int rf_zmq_send_timed_multi(void*  h,
         }
 
         // Scale according to current gain
-        // TODO: document baseband scaling for ZMQ with gain settings, etc. before enabling
-        // srsran_vec_sc_prod_cfc(buf, tx_gain, buf, nsamples_baseband);
+         srsran_vec_sc_prod_cfc(buf, tx_gain, buf, nsamples_baseband);
 
         // Finally, transmit baseband
         int n = rf_zmq_tx_baseband(&handler->transmitter[i], buf, nsamples_baseband);