Unfortunately, you cannot programmatically call an inbound-endpoint like that.
However the same functionality can be achieved using the Mule requester module:
Example:
<flow name="RequestFile" doc:name="RequestFile">
<http:inbound-endpoint exchange-pattern="request-response" host="localhost" port="8081" path="requestfile" doc:name="HTTP"/>
<mulerequester:request config-ref="Mule_Requester" resource="file:///s/tmp/demorequester/read/#[message.inboundProperties['filename']]" returnClass="java.lang.String" doc:name="Request a file"/>
</flow>
Instructions here: https://github.com/mulesoft/mule-module-requester and https://blogs.mulesoft.com/dev/mule-dev/introducing-the-mule-requester-module/