tcp: tcp_set_skb_tso_segs() no longer need struct sock parameter

tcp_set_skb_tso_segs() & tcp_init_tso_segs() no longer
use the sock pointer.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>