ipmi: ssif_bmc: fix message desynchronization after truncated response

A truncated response, caused by host power-off, or other conditions,
can lead to message desynchronization.

Raw trace data (STOP loss scenario, add state transition comment):

1. T-1: Read response phase (SSIF_RES_SENDING)
8271.955342 WR_RCV [03] <- Read polling cmd
8271.955348 RD_REQ [04] <== SSIF_RES_SENDING <- start sending response
8271.955436 RD_PRO [b4]
8271.955527 RD_PRO [00]
8271.955618 RD_PRO [c1]
8271.955707 RD_PRO [00]
8271.955814 RD_PRO [ad] <== SSIF_RES_SENDING <- last byte
<- !! STOP lost (truncated response)

2. T: New Write request arrives, BMC still in SSIF_RES_SENDING
8271.967973 WR_REQ [] <== SSIF_RES_SENDING >> SSIF_ABORTING <- log: unexpected WR_REQ in RES_SENDING
8271.968447 WR_RCV [02] <== SSIF_ABORTING <- do nothing
8271.968452 WR_RCV [02] <== SSIF_ABORTING <- do nothing
8271.968454 WR_RCV [18] <== SSIF_ABORTING <- do nothing
8271.968456 WR_RCV [01] <== SSIF_ABORTING <- do nothing
8271.968458 WR_RCV [66] <== SSIF_ABORTING <- do nothing
8271.978714 STOP [] <== SSIF_ABORTING >> SSIF_READY <- log: unexpected SLAVE STOP in state=SSIF_ABORTING

3. T+1: Next Read polling, treated as a fresh transaction
8271.979125 WR_REQ [] <== SSIF_READY >> SSIF_START
8271.979326 WR_RCV [03] <== SSIF_START >> SSIF_SMBUS_CMD <- smbus_cmd=0x03
8271.979331 RD_REQ [04] <== SSIF_RES_SENDING <- sending response
8271.979427 RD_PRO [b4] <- !! this is T's stale response -> desynchronization

When in SSIF_ABORTING state, a newly arrived command should still be
handled to avoid dropping the request or causing message
desynchronization.

Fixes: dd2bc5cc9e25 ("ipmi: ssif_bmc: Add SSIF BMC driver")
Signed-off-by: Jian Zhang <zhangjian.3032@bytedance.com>
Message-ID: <20260403090603.3988423-3-zhangjian.3032@bytedance.com>
Signed-off-by: Corey Minyard <corey@minyard.net>