net: remove redundant check in ip_metrics_convert()

Now ip_metrics_convert() is only called by ip_fib_metrics_init(). Before
ip_fib_metrics_init() invokes ip_metrics_convert(), it checks whether
input parameter fc_mx is NULL. Therefore, ip_metrics_convert() doesn't
need to check fc_mx.
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20221104022513.168868-1-shaozhengchao@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/metrics.c

@@ -14,9 +14,6 @@ static int ip_metrics_convert(struct net *net, struct nlattr *fc_mx,
 	struct nlattr *nla;
 	int remaining;
 
-	if (!fc_mx)
-		return 0;
-
 	nla_for_each_attr(nla, fc_mx, fc_mx_len, remaining) {
 		int type = nla_type(nla);
 		u32 val;