[NET]: fix __sk_stream_mem_reclaim

__sk_stream_mem_reclaim is only called by sk_stream_mem_reclaim.

As such the check on sk->sk_forward_alloc is not needed and can be
removed.

Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>