[NET]: Compact sk_stream_mem_schedule() code

This function references sk->sk_prot->xxx for many times.
It turned out, that there's so many code in it, that gcc
cannot always optimize access to sk->sk_prot's fields.

After saving the sk->sk_prot on the stack and comparing
disassembled code, it turned out that the function became
~10 bytes shorter and made less dereferences (on i386 and
x86_64). Stack consumption didn't grow.

Besides, this patch drives most of this function into the
80 columns limit.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>