net: fix crash when config small gso_max_size/gso_ipv4_max_size

In the Linux kernel, the following vulnerability has been resolved:

net: fix crash when config small gso_max_size/gso_ipv4_max_size

Config a small gso_max_size/gso_ipv4_max_size will lead to an underflow

in sk_dst_gso_max_size(), which may trigger a BUG_ON crash,

because sk->sk_gso_max_size would be much bigger than device limits.

Call Trace:

tcp_write_xmit

tso_segs = tcp_init_tso_segs(skb, mss_now);

tcp_set_skb_tso_segs

tcp_skb_pcount_set

// skb->len = 524288, mss_now = 8

// u16 tso_segs = 524288/8 = 65535 -> 0

tso_segs = DIV_ROUND_UP(skb->len, mss_now)

BUG_ON(!tso_segs)

Add check for the minimum value of gso_max_size and gso_ipv4_max_size.