MAINTAINERS: Add entry for rdma migration

MAINTAINERS: Add entry for rdma migration

It's not obvious to many that RDMA migration is in Odd Fixes stage for a
long time.  Add an explicit sub entry for it (besides migration, which
already covers the rdma files) to be clear on that, meanwhile add Zhijian
as Reviewer, so Zhijian can see the patches and review when he still has
the bandwidth.

Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Zhijian Li (Fujitsu) <lizhijian@fujitsu.com>
Cc: Fabiano Rosas <farosas@suse.de>
Acked-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20230925133441.265455-1-peterx@redhat.com>