include/feeds.mk: fix distfeeds.conf without per-feed repos

commit 514a4b3e1b4e4 ("include/feeds.mk: rework generation of opkg
distfeeds.conf") made the per-feed "base" repo unconditional, making
the default configuration fail when PER_FEED_REPO is disabled:

 root@wrt1900ac-1:~# cat /etc/opkg/distfeeds.conf
 src/gz openwrt_core http://openwrt.mork.no/18.06.0/targets/mvebu/cortexa9/packages
 src/gz openwrt_base http://openwrt.mork.no/18.06.0/packages/arm_cortex-a9_vfpv3/base
 root@wrt1900ac-1:~# opkg update
 Downloading http://openwrt.mork.no/18.06.0/targets/mvebu/cortexa9/packages/Packages.gz
 Updated list of available packages in /var/opkg-lists/openwrt_core
 Downloading http://openwrt.mork.no/18.06.0/targets/mvebu/cortexa9/packages/Packages.sig
 Signature check passed.
 Downloading http://openwrt.mork.no/18.06.0/packages/arm_cortex-a9_vfpv3/base/Packages.gz
 *** Failed to download the package list from http://openwrt.mork.no/18.06.0/packages/arm_cortex-a9_vfpv3/base/Packages.gz

 Collected errors:
  * opkg_download: Failed to download http://openwrt.mork.no/18.06.0/packages/arm_cortex-a9_vfpv3/base/Packages.gz, wget returned 8.

Cc: Matthias Schiffer <[email protected]>
Fixes: 514a4b3e1b4e ("include/feeds.mk: rework generation of opkg distfeeds.conf")
Signed-off-by: Bjørn Mork <[email protected]>
[whitespace/indentation fix]
Signed-off-by: Jo-Philipp Wich <[email protected]>

include/feeds.mk

@@ -34,8 +34,8 @@ endef
 define FeedSourcesAppend
 ( \
   echo 'src/gz %d_core %U/targets/%S/packages'; \
-  echo 'src/gz %d_base %U/packages/%A/base'; \
   $(strip $(if $(CONFIG_PER_FEED_REPO), \
+	echo 'src/gz %d_base %U/packages/%A/base'; \
 	$(foreach feed,$(FEEDS_AVAILABLE), \
 		$(if $(CONFIG_FEED_$(feed)), \
 			echo '$(if $(filter m,$(CONFIG_FEED_$(feed))),# )src/gz %d_$(feed) %U/packages/%A/$(feed)';)))) \