libosmocore: Add dependency for libmnl

Since libosmocore.git 53a2fde368d0161a38bc096d121ef61a9afbbe94,
libosmocore depends by default on libmnl.
Let's make sure to depend on it in the recipe to avoid recipe build
breakage.

Change-Id: I62221706b010766af5eed77a08693e877a197c7f
diff --git a/recipes-osmocom/libosmocore/libosmocore.inc b/recipes-osmocom/libosmocore/libosmocore.inc
index 40a42bc..ed1caa0 100644
--- a/recipes-osmocom/libosmocore/libosmocore.inc
+++ b/recipes-osmocom/libosmocore/libosmocore.inc
@@ -12,9 +12,11 @@
     gnutls \
     libusb \
     libsctp \
+    libmnl \
     "
 PACKAGECONFIG[gnutls] = "--enable-gnutls,--disable-gnutls,gnutls,"
 PACKAGECONFIG[libusb] = "--enable-libusb,--disable-libusb,libusb,"
 PACKAGECONFIG[libsctp] = "--enable-libsctp,--disable-libsctp,lksctp-tools,"
+PACKAGECONFIG[libmnl] = "--enable-libmnl,--disable-libmnl,libmnl,"
 
 inherit autotools pkgconfig