net_ipmi: initialize ipmiNetworkInstance to zero as default value

Close session failed like

```
Close Session command failed: Unspecified error
```

due to using `closeOtherNetInstanceSession` instead of
`closeMyNetInstanceSession`.

After initializing ipmiNetworkInstance to zero by default, the issue is
resolved.

Tested:
Ran the following multiple times
```
for ((i=0; i<10; i++)); do
  ./ipmitool -I lanplus -H $IP_ADDRESS%usb0 \
    -U root -P 0penBmc fru &
done
...

Before the change it will failed to close the session and run out of
available sessions.

For example,
```
Close Session command failed: Unspecified error
```

```
Error: Unable to establish IPMI v2 / RMCP+ session
```

After this change, no more errors and all close/create sessions are
successful.

Change-Id: Ibaf26fb2e554fa530542587b380891ee6f60ec0d
Signed-off-by: Willy Tu <wltu@google.com>
1 file changed