migration: Prioritize RDMA in ram_save_target_page()

migration: Prioritize RDMA in ram_save_target_page()

Address an error in RDMA-based migration by ensuring RDMA is prioritized
when saving pages in `ram_save_target_page()`.

Previously, the RDMA protocol's page-saving step was placed after other
protocols due to a refactoring in commit bc38dc2f5f3. This led to migration
failures characterized by unknown control messages and state loading errors
destination:
(qemu) qemu-system-x86_64: Unknown control message QEMU FILE
qemu-system-x86_64: error while loading state section id 1(ram)
qemu-system-x86_64: load of migration failed: Operation not permitted
source:
(qemu) qemu-system-x86_64: RDMA is in an error state waiting migration to abort!
qemu-system-x86_64: failed to save SaveStateEntry with id(name): 1(ram): -1
qemu-system-x86_64: rdma migration: recv polling control error!
qemu-system-x86_64: warning: Early error. Sending error.
qemu-system-x86_64: warning: rdma migration: send polling control error

RDMA migration implemented its own protocol/method to send pages to
destination side, hand over to RDMA first to prevent pages being saved by
other protocol.

Fixes: bc38dc2f5f3 ("migration: refactor ram_save_target_page functions")
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Message-ID: <20250305062825.772629-2-lizhijian@fujitsu.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>