This avoids another inderect call per RX packet which save us around
20-40 ns.

Changelog:

v1 -> v2:
- Move declaraions to fib_rules.h to remove warnings
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Brian Vazquez <brianvv@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>