ospf6d: fix test_ospf6_gr_topo1 topotest

ospf6d: fix test_ospf6_gr_topo1 topotest

1. topo test failure seen in below mentioned step of execution with
routes not synced with ABR
ospf6_gr_topo1/test_ospf6_gr_topo1.py::test_gr_rt3 - AssertionError:
"rt1" JSON output mismatches the expected result.

2. as experimental, increasing the sleep interval(21),
cleared the above step but failed in the step
FAILED ospf6_gr_topo1/test_ospf6_gr_topo1.py::test_gr_rt5 -
AssertionError: "rt2" JSON output mismatches the expected result

fix:
tuning retry parameter in check_routers cleared the topotest.
so, changing default value of ospf6 ABR task delay to 5 seconds.

Signed-off-by: Punith Kumar S <punith.shivakumar@sophos.com>