rf_imp: fail opening RF altogether if specified device fails to open

we've had a few runs in the CI where opening the specified RF device
failed but the eNB/UE still continued to run, just picking the next available
run. This led to false-positive tests.

The policy should be that whenever the user specified a RF device to
be openend, and this device fails, the whole process should fail and
the application should exit.

The auto-detection mode is still available but only if no device name
is specified at all.

lib/src/phy/rf/rf_imp.c

@@ -93,9 +93,9 @@ const char* srsran_rf_get_devname(srsran_rf_t* rf)
 int srsran_rf_open_devname(srsran_rf_t* rf, const char* devname, char* args, uint32_t nof_channels)
 {
   rf->thread_gain_run = false;
-  /* Try to open the device if name is provided */
-  if (devname) {
-    if (devname[0] != '\0') {
+
+  // Try to open the device if name is provided
+  if (devname && devname[0] != '\0') {
     int i = 0;
     while (available_devices[i] != NULL) {
       if (!strcasecmp(available_devices[i]->name, devname)) {
@@ -104,21 +104,22 @@ int srsran_rf_open_devname(srsran_rf_t* rf, const char* devname, char* args, uin
       }
       i++;
     }
-      printf("Device %s not found. Switching to auto mode\n", devname);
-    }
-  }
-
-  /* If in auto mode or provided device not found, try to open in order of apperance in available_devices[] array */
+    // provided device not found, abort
+    return SRSRAN_ERROR;
+  } else {
+    // auto-mode, try to open in order of apperance in available_devices[] array
     int i = 0;
     while (available_devices[i] != NULL) {
       if (!available_devices[i]->srsran_rf_open_multi(args, &rf->handler, nof_channels)) {
         rf->dev = available_devices[i];
-      return 0;
+        return SRSRAN_SUCCESS;
       }
       i++;
     }
+  }
+
   ERROR("No compatible RF frontend found");
-  return -1;
+  return SRSRAN_ERROR;
 }
 
 const char* srsran_rf_name(srsran_rf_t* rf)