add a default case to handle the situation when the variables are not
initialized.
Furthermore, abort() if the snmp agent passes an invalid option to the
bridge module. As the option (SET, GET, GETNEXT, COMMIT, ROLLBACK) is
determined by the snmp agent based on the operation requested by user,
this behaviour is unlikely to be abused as a source for a DoS, but if
ever hit will likely reveal a problem in the snmp agent or bridge
module.
Approved by: bz (mentor)
a7250df1fb