[yocto] clarify instructions for package feed installation

[Peter A. Bigot]

Following the instructions in the 2.4.2 mega-manual section 4.21.4 I set
in local.conf:

     PACKAGE_FEED_URIS = "http://192.168.65.22/oe/rpi3-sumo"
     PACKAGE_FEED_BASE_PATHS = "rpm"
     PACKAGE_FEED_ARCHS = "noarch cortexa7hf_neon_vfpv4 raspberrypi3"

and run this command:

     bitbake package-index

This produces a repodata directory in the deploy/rpm directory, sibling
to the arch directories.

drwxr-xr-x 2 pab pab 516096 Mar 15 12:26 cortexa7hf_neon_vfpv4
drwxr-xr-x 2 pab pab  24576 Mar 15 12:55 noarch
drwxr-xr-x 2 pab pab 262144 Mar 15 12:26 raspberrypi3
drwxr-xr-x 2 pab pab   4096 Mar 15 15:02 repodata

However, the repo file generated by the PACKAGE_FEED variables causes
dnf on the target to fetch repodata from inside each arch directory:

192.168.65.117 - - [15/Mar/2018:14:03:18 -0500] "GET 
/oe/rpi3-sumo/rpm/noarch/repodata/repomd.xml HTTP/1.1" 404 481 "-" 
"dnf/2.7.5"
192.168.65.117 - - [15/Mar/2018:14:05:51 -0500] "GET 
/oe/rpi3-sumo/rpm/raspberrypi3/repodata/repomd.xml HTTP/1.1" 404 487 "-" 
"dnf/2.7.5"
192.168.65.117 - - [15/Mar/2018:14:05:51 -0500] "GET 
/oe/rpi3-sumo/rpm/cortexa7hf_neon_vfpv4/repodata/repomd.xml HTTP/1.1" 
404 496 "-" "dnf/2.7.5"

This doesn't work.  I end up having to change the repo file to eliminate
the architectures.

Is this a problem specific to RPM, or am I doing something wrong?

Thanks.

Peter