…c-net#16264)

What is the motivation for this PR?
Default route check in sanity is added by sonic-net#16235
It only supports single asic for now. But constraint for single asic in recover stage is missed
It would cause keyError in multi-asic if there is bgp sanity check failure

    def adaptive_recover(dut, localhost, fanouthosts, nbrhosts, tbinfo, check_results, wait_time):
        outstanding_action = None
        for result in check_results:
            if result['failed']:
                if result['check_item'] == 'interfaces':
                    action = _recover_interfaces(dut, fanouthosts, result, wait_time)
                elif result['check_item'] == 'services':
                    action = _recover_services(dut, result)
                elif result['check_item'] == 'bgp':
                    # If there is only default route missing issue, only need to re-announce routes to recover
>                   if ("no_v4_default_route" in result['bgp'] and len(result['bgp']) == 1 or
                        "no_v6_default_route" in result['bgp'] and len(result['bgp']) == 1 or
                        ("no_v4_default_route" in result['bgp'] and "no_v6_default_route" in result['bgp'] and
                         len(result['bgp']) == 2)):
E                        KeyError: 'bgp'

check_results = [{'bgp0': {'down_neighbors': ['2603:10e2:400:1::5', 'fc00::2']}, 'bgp3': {'down_neighbors': ['2603:10e2:400:1::6']}, 'check_item': 'bgp', 'failed': True, ...}]
dut        = <MultiAsicSonicHost vlab-08>
fanouthosts = {}
localhost  = <tests.common.devices.local.Localhost object at 0x77f1b9270a90>
nbrhosts   = {'ARISTA01T0': <EosHost VM0129>, 'ARISTA01T2': <EosHost VM0128>}
outstanding_action = None
result     = {'bgp0': {'down_neighbors': ['2603:10e2:400:1::5', 'fc00::2']}, 'bgp3': {'down_neighbors': ['2603:10e2:400:1::6']}, 'check_item': 'bgp', 'failed': True, ...}
tbinfo     = {'auto_recover': 'False', 'comment': 'Tests multi-asic virtual switch vm', 'conf-name': 'vms-kvm-four-asic-t1-lag', 'duts': ['vlab-08'], ...}
wait_time  = 30
How did you do it?
Add single asic constraint in recover

How did you verify/test it?
Run test