session: clean up session table when re-adding an existing application namespace

session: clean up session table when re-adding an existing application namespace

The app ns semantics allows the same app ns to be re-added with different
interface. For example,

app ns add id blue secret 1 if tap0
app ns add id blue secret 1 if tap1

If tap0 is bound to table 0 and tap1 is bound to tap1, we need to clean
up the existing session table and possibly allocate a new session table
for the app ns.

Type: fix

Change-Id: I566d621081b7cdbd7d0c481fda53953b39c26001
Signed-off-by: Steven Luong <[email protected]>