routing: fix mc blinded path behaviour. #16839

Job	Run time
RPC and mobile compilation check	2m 37s
lint code	2m 38s
check commits	2m 37s
check pinned dependencies (google.golang.org/grpc v1.59.0)	6s
sample configuration check	1m 28s
cross compilation	2m 38s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	3s
Sqlc check	1m 24s
run unit tests (btcd unit-cover)	2m 38s
run macOS itest	2m 39s
run unit tests (unit tags="kvdb_etcd")	2m 37s
check release notes updated	4s
run ubuntu itests (btcd, backend=btcd cover=1)	1m 3s
run unit tests (unit tags="kvdb_postgres")	2m 36s
run windows itest	2m 17s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	2m 36s
run unit tests (unit tags="kvdb_sqlite")	2m 38s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	2m 36s
run unit tests (btcd unit-race)	2m 38s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	2m 24s
run unit tests (unit-module)	1m 3s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	2m 32s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	2m 32s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	1m 27s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	2m 27s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	1m 6s
run ubuntu itests (neutrino, backend=neutrino cover=1)	1s
finish	4s
	51m 29s

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