net: wifi: Fix disconnect reason codes

The shell is printing "connected" while passing
the wrong password to connect command. If the status
value is 0, then only shell will print "connected."
The wrong password will disconnect the connection
with an unspecified reason code.

If the default value of the unspecified disconnect
reason code is 0, then status will print "connected."
By changing the default value to WIFI_STATUS_CONN_LAST_STATUS,
it will print the correct reason, like a failed request
with reason code.

Signed-off-by: Kapil Bhatt <kapil.bhatt@nordicsemi.no>