cosmetic: rx_send_auth_info(): decide error cause with switch()

Prepare for tweaking error handling in a subsequent patch: use switch() instead
of if().

Prepares-for: I90df7b255317df1e5d968e7ce3b9d2c404b98db8
Change-Id: I1f628aa9d62b778951726bebec8cf338444fc897
1 file changed