im-online: don't disable offending validators

frame/im-online/src/lib.rs

@@ -101,7 +101,7 @@ use sp_runtime::{
 	PerThing, Perbill, Permill, RuntimeDebug, SaturatedConversion,
 };
 use sp_staking::{
-	offence::{Kind, Offence, ReportOffence},
+	offence::{DisableStrategy, Kind, Offence, ReportOffence},
 	SessionIndex,
 };
 use sp_std::prelude::*;
@@ -951,6 +951,10 @@ impl<Offender: Clone> Offence<Offender> for UnresponsivenessOffence<Offender> {
 		self.session_index
 	}
 
+	fn disable_strategy(&self) -> DisableStrategy {
+		DisableStrategy::Never
+	}
+
 	fn slash_fraction(&self, offenders: u32) -> Perbill {
 		// the formula is min((3 * (k - (n / 10 + 1))) / n, 1) * 0.07
 		// basically, 10% can be offline with no slash, but after that, it linearly climbs up to 7%

frame/im-online/src/tests.rs

@@ -56,6 +56,9 @@ fn test_unresponsiveness_slash_fraction() {
 		dummy_offence.slash_fraction(17),
 		Perbill::from_parts(46200000), // 4.62%
 	);
+
+	// Offline offences should never lead to being disabled.
+	assert_eq!(dummy_offence.disable_strategy(), DisableStrategy::Never);
 }
 
 #[test]