Add skip_4a_query_on_v6_linklocal_addr flag

Add a default ON flag so that the "don't send AAAA query when there is
only v6 link-local address with default route" feature can be disabled
by server push.

Bug: 256507503
Test: atest & manually set flag and check log
Change-Id: I46421fa8b2218be32ca2d25e9b37d6a67738dcb2