bonding: fix ns validation on backup slaves

When arp_validate is set to 2, 3, or 6, validation is performed for
backup slaves as well. As stated in the bond documentation, validation
involves checking the broadcast ARP request sent out via the active
slave. This helps determine which slaves are more likely to function in
the event of an active slave failure.

However, when the target is an IPv6 address, the NS message sent from
the active interface is not checked on backup slaves. Additionally,
based on the bond_arp_rcv() rule b, we must reverse the saddr and daddr
when checking the NS message.

Note that when checking the NS message, the destination address is a
multicast address. Therefore, we must convert the target address to
solicited multicast in the bond_get_targets_ip6() function.

Prior to the fix, the backup slaves had a mii status of "down", but
after the fix, all of the slaves' mii status was updated to "UP".

Fixes: 4e24be01 ("bonding: add new parameter ns_targets")
Reviewed-by: Jonathan Toppins <jtoppins@redhat.com>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>