bondutils: caching min_links value

bondutils: caching min_links value

Ticket: CM-13996
Reviewed By: Roopa, Nikhil G
Testing Done:

With the following configuration:
auto bond0
iface bond0
      bond-min-links	1
      bond-mode	802.3ad
      bond-slaves	eth0 eth1 eth2
      bond-xmit-hash-policy	layer3+4

auto vlan0
iface vlan0
      vlan-raw-device   bond0
      address 10.132.253.4/31
      address 2a03:2260:2342:fe09::1/126

On non cumulus distribution bond-min-links doesn't default to 1
For some reasons the min_links value wasn't cache with the other
bond values, if you issue an ifreload on a running/existing configuration
since the min_links value is not cache ifreload will down the bond, set
min_links to 1, then bond up. When taking the bond down the kernel will
also flush the ipv6 address but not the ipv4 address...

The issue was reported by an ifupdown2 contributor on github. He find out
that when running ifreload the ipv6 were flushed.

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>