netfilter: nf_conntrack: remove exceptional & on function name

In this file, function names are otherwise used as pointers without &.

A simplified version of the Coccinelle semantic patch that makes this
change is as follows:

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

f(...) { ... }

@@
identifier r.f;
@@

- &f
+ f
// </smpl>

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>