protobuf: add missing default case to enum (#6870)
protobuf: add missing default case to enum (#6870)

Description: Switch statements on enums should have a default case, see https://google.github.io/styleguide/cppguide.html#Loops_and_Switch_Statements.
Risk Level: Low
Testing: Ran bazel test source/common/protobuf/…
Docs Changes: N/A
Release Notes: N/A

Signed-off-by: Frank Fort <fdfbceb5ed4073410ce08fbd0f7c033bb477f889@google.com>
eklitzke/envoy,istio/envoy,eklitzke/envoy,istio/envoy,lyft/envoy,envoyproxy/envoy,jrajahalme/envoy,eklitzke/envoy,envoyproxy/envoy-wasm,lizan/envoy,envoyproxy/envoy,istio/envoy,lizan/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,istio/envoy,jrajahalme/envoy,lizan/envoy,lyft/envoy,lyft/envoy,eklitzke/envoy,lyft/envoy,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,eklitzke/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,eklitzke/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,jrajahalme/envoy,istio/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,jrajahalme/envoy,lizan/envoy,envoyproxy/envoy,lyft/envoy,lizan/envoy,jrajahalme/envoy,envoyproxy/envoy,jrajahalme/envoy,istio/envoy,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy