if_sk patch to get more info from people with problems

[User Valera]

#dmesg | grep sk
skc0: <Marvell Gigabit Ethernet> port 0xd800-0xd8ff mem 
0xfeafc000-0xfeafffff irq 22 at device 5.0 on pci2
skc0: Yukon Gigabit Ethernet 10/100/1000Base-T Adapter
skc0: PN: Yukon 88E8001
skc0: EC: Rev. 1.3
skc0: MN: Marvell
skc0: SN: AbCdEfG334454
sk0: <Marvell Semiconductor, Inc. Yukon> on skc0
sk0: Ethernet address: 00:11:2f:54:07:95
miibus0: <MII bus> on sk0

I can 100% reproduce the my problem by follows
ftp throw sk0 on another host
get file

transfer speed starting at ~10MB/s monotonly decresing down to ~60KB/s 
(in 1-2 minutes)
netstat -I sk0 -w 1 -- show no errors but only decrising speed

Syptoms (from my point if view) very similar to SACK issue which (as i 
think)
i expirienced during last week but diferences in two moments:
1) before - transfer speed have decrising down to --stalled--
2) i have another interface fxp0 which now (after declared SACK issue 
resolved)
    working without problems

my local cure was  - debug.mpsafenet="0"
it have worked last week and worked now (transfer speed is ~10MB/s)

You can ask me about any information/action which can help resolve the 
problem - i will help as i can.

Valera.