migration: Handle migration_incoming_setup() errors consistently

migration: Handle migration_incoming_setup() errors consistently

Commit b673eab4e2 "multifd: Make multifd_load_setup() get an Error
parameter" changed migration_incoming_setup() to take an Error **
argument, and adjusted the callers accordingly.  It neglected to
change adjust multifd_load_setup(): it still exit()s on error.  Clean
that up.

The error now gets propagated up two call chains: via
migration_fd_process_incoming() to rdma_accept_incoming_migration(),
and via migration_ioc_process_incoming() to
migration_channel_process_incoming().  Both chain ends report the
error with error_report_err(), but otherwise ignore it.  Behavioral
change: we no longer exit() on this error.

This is consistent with how we handle other errors here, e.g. from
multifd_recv_new_channel() via migration_ioc_process_incoming() to
migration_channel_process_incoming().  Whether it's consistently right
or consistently wrong I can't tell.

Also clean up the return value from the unusual 0 on success, 1 on
error to the more common true on success, false on error.

Cc: Juan Quintela <quintela@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210720125408.387910-11-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@ionos.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>