ipv6: drop unneeded goto

Delete jump to a label on the next line, when that label is not
used elsewhere.

A simplified version of the semantic patch that makes this change is as
follows: (http://coccinelle.lip6.fr/

)

// <smpl>
@r@
identifier l;
@@

-if (...) goto l;
-l:
// </smpl>

Also remove the unnecessary ret variable.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>