Add alias as prefix for flavor_rxtx v3

As v3 api rules, the extended attribute should be with extension
alias as prefix. So fix this case for flavor-rxtx v3 extension.

Closes-bug: 1252986
DocImpact

Change-Id: I9f5984a406d039245db4bef2df53cfe10a331cc2
Merge "Add alias as prefix for flavor_rxtx v3"