#2319 Certain agentx failures can result in apparent agent hang

[Bill Fenner]

The failure that I experienced was obscure, but may not be the only way to experience it. While trying to muddle through being able to gracefully handle [the obsolete type] UInteger32 varbinds in set requests to AgentX subagents, I got into a state where agentx_build_varbind would return failure:

trace: agentx_realloc_build_varbind(): mibgroup/agentx/protocol.c, 570:
agentx_build_varbind: unknown type 71 (0x47)
trace: _sess_async_send(): snmp_api.c, 4892:
sess_async_send: encoding failure

All future requests to the agent got:

snmp_agent: request queued while processing set, asp = 0xf7eafa68

because netsnmp_processing_set is never cleared in this failure path.