snmp: probing parser returns unknown if not enough data

Ticket: 7019

rust/src/snmp/snmp.rs

@@ -361,7 +361,7 @@ unsafe extern "C" fn snmp_probing_parser(_flow: *const Flow,
     }
     let slice = build_slice!(input,input_len as usize);
     let alproto = ALPROTO_SNMP;
-    if slice.len() < 4 { return ALPROTO_FAILED; }
+    if slice.len() < 4 { return ALPROTO_UNKNOWN; }
     match parse_pdu_envelope_version(slice) {
         Ok((_,_))               => alproto,
         Err(Err::Incomplete(_)) => ALPROTO_UNKNOWN,