Add 5G icon in manual network selection.

Manual network selection need to have 5G icon when 5G signal is
available.

Bug: 143995814
Test: 1. Build pass.
2. check UI:
3-1. Open APN settings page: Settings > Network & Internet > Mobile Network > Advanced > Access Point Names
3-2. Turn off Automatically select network

Change-Id: I3664105d3bf52e3694a2274c6aa76a755de4e1dd

src/com/android/settings/network/telephony/NetworkOperatorPreference.java

@@ -187,6 +187,9 @@ public class NetworkOperatorPreference extends Preference {
             return mShow4GForLTE
                     ? R.drawable.ic_signal_strength_4g : R.drawable.signal_strength_lte;
         }
+        if (ci instanceof CellInfoNr) {
+            return R.drawable.signal_strength_5g;
+        }
         return MobileNetworkUtils.NO_CELL_DATA_TYPE_ICON;
     }