ipv4: remove unnecessary judgment in ip_route_output_key_hash_rcu

In the ip_route_output_key_cash_rcu function, the input fl4 member saddr is
first checked to be non-zero before entering multicast, broadcast and
arbitrary IP address checks. However, the fact that the IP address is not
0 has already ruled out the possibility of any address, so remove
unnecessary judgment.

Signed-off-by: Zhengchao Shao <shaozhengchao@163.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250409033321.108244-1-shaozhengchao@163.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>