enb: fix AWGN config example and help message

we've moved to SNR rather than channel noise so this fixes the example and help text

srsenb/enb.conf.example

@@ -184,7 +184,7 @@ enable = false
 #
 # -- AWGN Generator
 # awgn.enable:       Enable/disable AWGN generator
-# awgn.n0:           Noise power in dBfs
+# awgn.snr:          Target SNR in dB
 #
 # -- Fading emulator
 # fading.enable:     Enable/disable fading simulator
@@ -214,7 +214,7 @@ enable = false
 
 [channel.dl.awgn]
 #enable        = false
-#n0            = -30
+#snr            = 30
 
 [channel.dl.fading]
 #enable        = false

srsenb/src/main.cc

@@ -150,7 +150,7 @@ void parse_args(all_args_t* args, int argc, char* argv[])
     /* Downlink Channel emulator section */
     ("channel.dl.enable",            bpo::value<bool>(&args->phy.dl_channel_args.enable)->default_value(false),               "Enable/Disable internal Downlink channel emulator")
     ("channel.dl.awgn.enable",       bpo::value<bool>(&args->phy.dl_channel_args.awgn_enable)->default_value(false),          "Enable/Disable AWGN simulator")
-    ("channel.dl.awgn.snr",          bpo::value<float>(&args->phy.dl_channel_args.awgn_snr_dB)->default_value(30.0f),         "Noise level in decibels full scale (dBfs)")
+    ("channel.dl.awgn.snr",          bpo::value<float>(&args->phy.dl_channel_args.awgn_snr_dB)->default_value(30.0f),         "Target SNR in dB")
     ("channel.dl.fading.enable",     bpo::value<bool>(&args->phy.dl_channel_args.fading_enable)->default_value(false),        "Enable/Disable Fading model")
     ("channel.dl.fading.model",      bpo::value<string>(&args->phy.dl_channel_args.fading_model)->default_value("none"),      "Fading model + maximum doppler (E.g. none, epa5, eva70, etu300, etc)")
     ("channel.dl.delay.enable",      bpo::value<bool>(&args->phy.dl_channel_args.delay_enable)->default_value(false),         "Enable/Disable Delay simulator")