Bug discussion:Tcp snd_nxt will not be increased.

[Li, Qing]

Hi,

Could you please tell us what version you are running?

>
> If the tcp_output just have some error, for example: when alloc mbuf,
> it returns NULL, and then the snd_nxt number will not be return to
> normal.
> If just in this time, SYN Ack arrives, freeBSD can't handle this
> situdition.
>

I have seen a related issue in older versions that I fixed, but it's from 
the SYN+ACK perspective. If my memory serves me right, local listener receives
a SYN packet, transmits the SYN+ACK, but memory allocation fails, so the
SYN+ACK packet was never transmitted onto the wire, however, the SEQ advanced
by 1. As a result of SEQ update, the retransmitted SYN packet from the other 
end were discard as duplicates, eventually the connection times out.

-- Qing