fib: fix fib_rule_ops indirect call wrappers when CONFIG_IPV6=m

If CONFIG_IPV6=m, the IPV6 functions won't be found by the linker:

ld: net/core/fib_rules.o: in function `fib_rules_lookup':
fib_rules.c:(.text+0x606): undefined reference to `fib6_rule_match'
ld: fib_rules.c:(.text+0x611): undefined reference to `fib6_rule_match'
ld: fib_rules.c:(.text+0x68c): undefined reference to `fib6_rule_action'
ld: fib_rules.c:(.text+0x693): undefined reference to `fib6_rule_action'
ld: fib_rules.c:(.text+0x6aa): undefined reference to `fib6_rule_suppress'
ld: fib_rules.c:(.text+0x6bc): undefined reference to `fib6_rule_suppress'
make: *** [Makefile:1166: vmlinux] Error 1

Reported-by: Sven Joachim <svenjoac@gmx.de>
Fixes: b9aaec8f ("fib: use indirect call wrappers in the most common fib_rules_ops")
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: Brian Vazquez <brianvv@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>