osmocom: Introduce META_TELEPHONY_OSMO_INC to easily bump version

For libosmocore updates we need a nice way to rebuild all libraries
using it. This can be done using the META_TELEPHONY_OSMO_INC variable.
diff --git a/recipes-osmocom/openbsc/openbsc.inc b/recipes-osmocom/openbsc/openbsc.inc
index 44b0935..4fbb14b 100644
--- a/recipes-osmocom/openbsc/openbsc.inc
+++ b/recipes-osmocom/openbsc/openbsc.inc
@@ -9,7 +9,7 @@
 SRC_URI = "file://osmo-nitb.init \
 	   file://osmo-bsc_mgcp.init \
 	   file://osmo-bsc.init"
-INC_PR = "r11"
+INC_PR = "r11.${META_TELEPHONY_OSMO_INC}"
 
 
 EXTRA_OECONF += " --enable-nat --enable-osmo-bsc "