Add UDP protocol by default in SNMP client

Set UDP protocol as transport protocol by default on Client
instantiation.

Tested: protocol set as UDP by default when creating subscribers.

```
busctl call xyz.openbmc_project.Network.SNMP /xyz/openbmc_project/network/snmp/manager xyz.openbmc_project.Network.Client.Create Client sq 192.168.1.25 999
s "/xyz/openbmc_project/network/snmp/manager/1"

busctl get-property xyz.openbmc_project.Network.SNMP /xyz/openbmc_project/network/snmp/manager/1 xyz.openbmc_project.Network.Client Address
s "192.168.1.25"

busctl get-property xyz.openbmc_project.Network.SNMP /xyz/openbmc_project/network/snmp/manager/1 xyz.openbmc_project.Network.Client TransportProtocol
s "xyz.openbmc_project.Network.Client.TransportProtocol.UDP"
```

Change-Id: I21aa601519cbfa51db3b21d260e77c46e6383ae7
Signed-off-by: Ivan Mikhaylov <fr0st61te@gmail.com>
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
2 files changed