selftests: Add fib-onlink-tests.sh to TEST_PROGS

Fixes: 153e1b84

 ("selftests: Add FIB onlink tests")
Reported-by: Ido Schimmel <idosch@idosch.org>
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>