selftests: bonding: use slowwait instead of hard code sleep

Use slowwait instead of hard code sleep for bonding tests.

In function setup_prepare(), the client_create() will be called after
server_create(). So I think there is no need to sleep in server_create()
and remove it.

For lab_lib.sh, remove bonding module may affect other running bonding tests.
And some test env may buildin bond which can't be removed. The bonding
link should be removed by lag_reset_network() or netns delete.

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://lore.kernel.org/r/20240205130048.282087-5-liuhangbin@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>