migration: qmp_migrate(): keep working after syntax error

If a user or QMP client enter a bad syntax for the migrate
command in QMP/HMP, then the migrate command will never succeed
from that point on.

For example, if you enter:

(qemu) migrate tcp;0:4444
migrate: Parameter 'uri' expects a valid migration protocol

Then the migrate command will always fail from now on:

(qemu) migrate tcp:0:4444
migrate: There's a migration process in progress

The problem is that qmp_migrate() sets the migration status to
MIG_STATE_SETUP and doesn't reset it on syntax error. This bug
was introduced by commit 29ae8a4.

Reviewed-by: Michael R. Hines <mrhines@us.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
(cherry picked from commit c950114)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

migration.c

@@ -437,6 +437,7 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
 #endif
     } else {
         error_set(errp, QERR_INVALID_PARAMETER_VALUE, "uri", "a valid migration protocol");
+        s->state = MIG_STATE_ERROR;
         return;
     }