ip: bond: add peer notification delay support

ip: bond: add peer notification delay support

Ability to tweak the delay between gratuitous ND/ARP packets has been
added in kernel commit 07a4ddec3ce9 ("bonding: add an option to
specify a delay between peer notifications"), through
IFLA_BOND_PEER_NOTIF_DELAY attribute. Add support to set and show this
value.

Example:

    $ ip -d link set bond0 type bond peer_notify_delay 1000
    $ ip -d link l dev bond0
    2: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue
    state UP mode DEFAULT group default qlen 1000
        link/ether 50:54:33:00:00:01 brd ff:ff:ff:ff:ff:ff
        bond mode active-backup active_slave eth0 miimon 100 updelay 0
    downdelay 0 peer_notify_delay 1000 use_carrier 1 arp_interval 0
    arp_validate none arp_all_targets any primary eth0
    primary_reselect always fail_over_mac active xmit_hash_policy
    layer2 resend_igmp 1 num_grat_arp 5 all_slaves_active 0 min_links
    0 lp_interval 1 packets_per_slave 1 lacp_rate slow ad_select
    stable tlb_dynamic_lb 1 addrgenmode eu

Signed-off-by: Vincent Bernat <vincent@bernat.ch>
Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David Ahern <dsahern@gmail.com>