[snmp] slow snmp v3 discovery timeout

[Josh Bers]

In working with snmpv3 contexts, I've found that sending a Pdu request to an
agent is not there takes a long time to return ~19 seconds. When I looked
into the code, it looks as though the v3 context is using a UsmDiscoveryBean
to discover the v3 engineid and other parameters if that agent has never
been contacted. The bean class uses the default timeout when sending the Pdu
request for discovery. However, I had set a different retry_array on the
original Pdu that is causing the discovery to be sent in the first place. It
would make sense for the stack to use this retry array when sending the
discovery Pdu as well. Or at a minimum provide a way to change the default
retry array for v3 discovery. Perhaps there is another way to do this that
won't take so long that I am missing.. suggestions welcome.
 
 
Josh