osmo-iuh: workaround oe-core forcing fail of sctp.h autoconf check

oe-core is currently (pyro and current master) forcing non-availability
of netinet/sctp.h header file through autoconf's export CONFIG_SITE
pointing to files in meta/site/, which contain:
ac_cv_header_netinet_sctp_h=${ac_cv_header_netinet_sctp_h=no}

As a result, netinet/sctp.h is not found despite DEPENDS="lksctp-tools"
and the file being available correctly under recipe-sysroot/ and finally
configure fails with AC_MSG_ERROR().

It was confirmed by OE devs that those lines should not be there, and a
patch has been submitted:
https://patchwork.openembedded.org/patch/168892/

Since it's not available in pyro nor latest release, let's workaround it
in our recipe to make sure it works with older versions of OE.

Change-Id: Ic54c50300bcf2cd278db95550d14eef044caea05
diff --git a/recipes-osmocom/osmo-iuh/osmo-iuh.inc b/recipes-osmocom/osmo-iuh/osmo-iuh.inc
index ab412ad..92b4633 100644
--- a/recipes-osmocom/osmo-iuh/osmo-iuh.inc
+++ b/recipes-osmocom/osmo-iuh/osmo-iuh.inc
@@ -3,9 +3,13 @@
 LICENSE = "AGPLv3"
 LIC_FILES_CHKSUM = "file://COPYING;md5=73f1eb20517c55bf9493b7dd6e480788"
 
-DEPENDS = "libosmocore libosmo-netif libosmo-sccp libasn1c"
+DEPENDS = "libosmocore libosmo-netif libosmo-sccp libasn1c lksctp-tools"
 
-INC_PR="r1.${META_TELEPHONY_OSMO_INC}"
+INC_PR="r2.${META_TELEPHONY_OSMO_INC}"
+
+# Workaround to oe-core meta/site/* CONFIG_SITE files passed to autoconf forcing unavailability of netinet/sctp.h.
+# Patch fixing issue upstream: https://patchwork.openembedded.org/patch/168892/
+CACHED_CONFIGUREVARS += "ac_cv_header_netinet_sctp_h=yes"
 
 inherit autotools pkgconfig systemd