ifupdown: install missing directories

There are four directories in which scripts can be placed which will
always be run for any interface during certain phases of ifup and ifdown
commands:
/etc/network/if-pre-up.d/
/etc/network/if-up.d/
/etc/network/if-down.d/
/etc/network/if-post-down.d/

Even if there are no scripts in these directories, ifup and ifdown
commands will also search these directories by using run-parts command.

Install these directories to fix the following runtime errors:
$ cat /etc/network/interfaces
auto lo
iface lo inet loopback
$ ifdown lo
ifdown: interface lo not configured
$ ifup lo
run-parts: failed to open directory /etc/network/if-up.d: No such file or directory
ifup: failed to bring up lo

(From OE-Core rev: 277bc7ab1fedd81f4df578e544ec381c819a10f9)

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/ifupdown/ifupdown_0.8.41.bb

@@ -42,6 +42,11 @@ do_install () {
 	install -m 0644 ifup.8 ${D}${mandir}/man8
 	install -m 0644 interfaces.5 ${D}${mandir}/man5
 	cd ${D}${mandir}/man8 && ln -s ifup.8 ifdown.8
+
+	install -d ${D}${sysconfdir}/network/if-pre-up.d
+	install -d ${D}${sysconfdir}/network/if-up.d
+	install -d ${D}${sysconfdir}/network/if-down.d
+	install -d ${D}${sysconfdir}/network/if-post-down.d
 }
 
 do_install_ptest () {