tcp: fix tcp_min_tso_segs sysctl

tcp_min_tso_segs is now stored in u8, so max value is 255.

255 limit is enforced by proc_dou8vec_minmax().

We can therefore remove the gso_max_segs variable.

Fixes: 47996b489bdc ("tcp: convert elligible sysctls to u8")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>