ANDROID: GKI: fix ABI breakage in struct ipv6_devconf

The following list of commits, which are in the 5.15.136 release, add a
new field in struct ipv6_devconf and this breaks the abi. Fix this by
using one of the reserved slots for upstream changes and update the stg
file to preserve the build.

  5e13e69d ("net: release reference to inet6_dev pointer")
  aade10d5 ("net: change accept_ra_min_rtr_lft to affect all RA lifetimes")
  8f12d2d6 ("net: add sysctl accept_ra_min_rtr_lft")

type 'struct ipv6_devconf' changed
  member 'union { struct { __s32 accept_ra_min_lft; u32 padding; }; struct { u64 android_kabi_reserved1; }; union { }; }' was added
  member 'u64 android_kabi_reserved1' was removed

Bug: 320243175
Change-Id: Icddcad574f3c29f6d3e63b10f8c7e51bdf46fe7f
Signed-off-by: Carlos Llamas <cmllamas@google.com>