Disable IPv6 RAs & Autoconf For All (Not Just Default)

Disable IPv6 RAs & Autoconf For All (Not Just Default)

The current kernel sysctl settings modify the
net.ipv6.conf.default.accept_ra and net.ipv6.conf.default.autoconf
to both be '0'. However, this is overridden by the settings in
net.ipv6.conf.all, so no matter what setting is in the ifcfg file
for the IPv6 interface, autoconfiguration and accept_ra will be
enabled. This causes a security vulnerability where rogue RAs
could be used to intercept traffic from the controllers.

This change sets both default and all settings to '0' for IPv6
accept_ra and autoconf.

Closes-Bug: 1632830
Change-Id: I95b86c5c6feed30dfa5103ffbddb9e85ac567bbb