ipv4: remove fib_info_devhash[]

ipv4: remove fib_info_devhash[]

Upcoming per-netns RTNL conversion needs to get rid
of shared hash tables.

fib_info_devhash[] is one of them.

It is unclear why we used a hash table, because
a single hlist_head per net device was cheaper and scalable.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20241004134720.579244-5-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>