ipv6: exthdrs: Remove redundant skb_headlen() check in ip6_parse_tlv().

ipv6_destopt_rcv() and ipv6_parse_hopopts() pulls these data

  - Hop-by-Hop/Destination Options Header : 8
  - Hdr Ext Len                           : skb_transport_header(skb)[1] << 3

and calls ip6_parse_tlv(), so it need not check if skb_headlen() is less
than skb_transport_offset(skb) + (skb_transport_header(skb)[1] << 3).

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/exthdrs.c

@@ -126,9 +126,6 @@ static bool ip6_parse_tlv(bool hopbyhop,
 		max_count = -max_count;
 	}
 
-	if (skb_transport_offset(skb) + len > skb_headlen(skb))
-		goto bad;
-
 	off += 2;
 	len -= 2;