Integrate libmnl (minimal netlink) library with libosmocore select loop

This adds an easy way to listen to netlink events form the Linux kernel
from within libosmocore applications.

The new dependency can be disabled via the "--disable-lbimnl" configure flag.

Change-Id: I4f787ee68f0d6d04f0a5655eb57d55b3b326a42f
diff --git a/contrib/jenkins_arm.sh b/contrib/jenkins_arm.sh
index c9cd922..e7df37d 100755
--- a/contrib/jenkins_arm.sh
+++ b/contrib/jenkins_arm.sh
@@ -20,6 +20,7 @@
 	--disable-shared \
 	--disable-libsctp \
 	--disable-libusb \
+	--disable-libmnl \
 	--enable-external-tests \
 	CFLAGS="-Os -ffunction-sections -fdata-sections -nostartfiles -nodefaultlibs $WERROR_FLAGS"