configure: Introduce --disable-libsctp and error by default if libsctp not found

This way libosmocore build fails during configuring phase if expected
default behavior (building with libsctp support enabled and providing
osmo_sock_init2_multiaddr() API) fails. User is still provided with
--disable-libsctp option in case he doesn't need those features or his
environment doesn't provide required libsctp APIs.

Change-Id: I710c9cb1c6da0e5fc94b792df8bf60194a72208f
diff --git a/contrib/jenkins_arm.sh b/contrib/jenkins_arm.sh
index e3a6cd1..8ee90f0 100755
--- a/contrib/jenkins_arm.sh
+++ b/contrib/jenkins_arm.sh
@@ -18,6 +18,7 @@
 	--enable-embedded \
 	--disable-doxygen \
 	--disable-shared \
+	--disable-libsctp \
 	--enable-external-tests \
 	CFLAGS="-Os -ffunction-sections -fdata-sections -nostartfiles -nodefaultlibs $WERROR_FLAGS"