rpc: Return incrementalrelayfee in getmempoolinfo

test/functional/feature_rbf.py

@@ -712,6 +712,7 @@ class ReplaceByFeeTest(BitcoinTestFramework):
 
         # Higher fee, higher feerate, different txid, but the replacement does not provide a relay
         # fee conforming to node's `incrementalrelayfee` policy of 1000 sat per KB.
+        assert_equal(self.nodes[0].getmempoolinfo()["incrementalrelayfee"], Decimal("0.00001"))
         tx.vout[0].nValue -= 1
         assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, tx.serialize().hex())