ipv6: sr: fix double free of skb after handling invalid SRH

The icmpv6_param_prob() function already does a kfree_skb(),
this patch removes the duplicate one.

Fixes: 1ababeba

 ("ipv6: implement dataplane support for rthdr type 4 (Segment Routing Header)")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David Lebrun <david.lebrun@uclouvain.be>
Signed-off-by: David S. Miller <davem@davemloft.net>