Discarded HTTPRouteFilter when multiple filters specified

[AlexKrudu]

Description:
Sometimes when there're multiple HTTPRouteFIlters specified for an HTTPRoute, some filters get discarded

Repro steps:
In the testdata
https://github.com/envoyproxy/gateway/blob/main/internal/gatewayapi/testdata/httproute-with-urlrewrite-hostname-filter.out.yaml#L336 should be an additional block of

host:
    header: my-host

since in route there are both host and path rewrite filters specified https://github.com/envoyproxy/gateway/blob/main/internal/gatewayapi/testdata/httproute-with-urlrewrite-hostname-filter.in.yaml#L119