fib: fix fib_rules_ops indirect calls wrappers

This patch fixes:
commit b9aaec8f ("fib: use indirect call wrappers in the most common
fib_rules_ops") which didn't consider the case when
CONFIG_IPV6_MULTIPLE_TABLES is not set.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: b9aaec8f ("fib: use indirect call wrappers in the most common fib_rules_ops")
Signed-off-by: Brian Vazquez <brianvv@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>