applier: filter incoming synchro packets via transaction initiator

Currently we use synchro packets filtration based on their contents,
in particular by their xrow->replica_id value. Still there was a
question if we can optimize this moment and rather filter out all
packets coming from non-leader replica.

Raft specification requires that only data from a current leader
should be applied to local WAL but doesn't put a concrete claim on
the data transport, ie how exactly rows are reaching replicas. This
implies that data propagation may reach replicas indirectly via transit
hops. Thus we drop applier->instance_id filtering and rely on
xrow->replica_id matching instead.

In the test (inspired by Serge Petrenko's test) we recreate the situation
where replica3 obtains master's node data (which is a raft leader)
indirectly via replica2 node.

Closes #6035

Co-developed-by: Serge Petrenko <sergepetrenko@tarantool.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>