bonding: show NS IPv6 targets in proc master info

bonding: show NS IPv6 targets in proc master info

When adding bond new parameter ns_targets. I forgot to print this
in bond master proc info. After updating, the bond master info will look
like:

ARP IP target/s (n.n.n.n form): 192.168.1.254
NS IPv6 target/s (XX::XX form): 2022::1, 2022::2

Fixes: 4e24be018eb9 ("bonding: add new parameter ns_targets")
Reported-by: Li Liang <liali@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://lore.kernel.org/r/20220530062639.37179-1-liuhangbin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>