selftests: bonding: do not test arp/ns target with mode balance-alb/tlb

The prio_arp/ns tests hard code the mode to active-backup. At the same
time, The balance-alb/tlb modes do not support arp/ns target. So remove
the prio_arp/ns tests from the loop and only test active-backup mode.

Fixes: 481b56e0

 ("selftests: bonding: re-format bond option tests")
Reported-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Closes: https://lore.kernel.org/netdev/17415.1705965957@famine/
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Link: https://lore.kernel.org/r/20240123075917.1576360-1-liuhangbin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>