netbase: fix file search path for 'interfaces' file

This .bbappend file is used to override the 'interfaces' file for certain
targets. The current version is broken in that it does not search the correct
path(s).

Thanks to Robert P. J. Day and Gary Thomas for spotting the issue and providing
patches.

Signed-off-by: Denys Dmytriyenko <denys@ti.com>

recipes-core/netbase/netbase_5.0.bbappend

@@ -1,3 +1 @@
-THISDIR := "${@os.path.dirname(bb.data.getVar('FILE', d, True))}"
-FILESPATH =. "${@base_set_filespath(["${THISDIR}/${PN}"], d)}:"
-
+FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}-${PV}:"