selftests: fib_tests: sleep after changing carrier. again.

Just like commit e2ba732a

 ("selftests: fib_tests: sleep after
changing carrier"), wait one second to allow linkwatch to propagate the
carrier change to the stack.

There are two sets of carrier tests. The first slept after the carrier
was set to off, and when the second set ran, it was likely that the
linkwatch would be able to run again without much delay, reducing the
likelihood of a race. However, if you run 'fib_tests.sh -t carrier' on a
loop, you will quickly notice the failures.

Sleeping on the second set of tests make the failures go away.

Cc: David Ahern <dsahern@gmail.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>