HAST instability

[Daniel Kalchev]

Decided to apply the patch proposed in -current by Mikolaj Golub: 
http://people.freebsd.org/~trociny/uipc_socket.c.patch

This apparently fixed my issue as well. Running without checksums for a 
full bonnie++ run (~100GB write/rewrite) produced no disconnects, no 
stalls and generated up to 280MB/sec (4 drives in stripped zpool). 
Interestingly, the hast devices write latency as observed by gstat was 
under 30ms.

I believe this fix should be committed.

Here are the accumulated netstat -s from both hosts, for comparison with 
previous runs. Retransmits etc are much less.

http://news.digsys.bg/~admin/hast/test3jun-fix/b1a-netstat-s
http://news.digsys.bg/~admin/hast/test3jun-fix/b1b-netstat-s
http://news.digsys.bg/~admin/hast/test3jun-fix/b1b-systat-if-fix

Before applying the patch I verified there are no network problems. 
Created 1TB file from /dev/random on the first host. Copied over to the 
second host with ftp. Transfer speed was low, at 80MB/sec -- ftp would 
utilize one CPU core 100% at the receiving node. Then calculated md5 
checksums on both sides, matched.

Daniel