RFC: ANDROID: net: ipv6: Flip FIB entries to fib6_info

Convert all code paths referencing a FIB entry from rt6_info
to fib6_info. Align with upstream commit 8d1c802b
("net/ipv6: Flip FIB entries to fib6_info") changes.

Fixes: Change-Id: I82d16e3737d9cdfa6489e649e247894d0d60cbb1
       ("ANDROID: net: ipv6: autoconf routes into per-device tables")
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>