ipv6: rpl: Remove redundant skb_dst_drop().

RPL code has a pattern where skb_dst_drop() is called before
ip6_route_input().

However, ip6_route_input() calls skb_dst_drop() internally,
so we need not call skb_dst_drop() before ip6_route_input().
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20230710213511.5364-1-kuniyu@amazon.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/exthdrs.c

@@ -612,8 +612,6 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
 
 	kfree(buf);
 
-	skb_dst_drop(skb);
-
 	ip6_route_input(skb);
 
 	if (skb_dst(skb)->error) {

net/ipv6/rpl_iptunnel.c

@@ -272,8 +272,6 @@ static int rpl_input(struct sk_buff *skb)
 	dst = dst_cache_get(&rlwt->cache);
 	preempt_enable();
 
-	skb_dst_drop(skb);
-
 	if (!dst) {
 		ip6_route_input(skb);
 		dst = skb_dst(skb);
@@ -284,6 +282,7 @@ static int rpl_input(struct sk_buff *skb)
 			preempt_enable();
 		}
 	} else {
+		skb_dst_drop(skb);
 		skb_dst_set(skb, dst);
 	}