libosmocore: Add libusb to DEPENDS

In I656a1a38cbb5b1f3a9145d2869d3b4d0adefcae3, libosmocore got libusb
integration support, and since then libusb is a dependency (which can be
disabled through --disable-libusb).

Related: OS#4299
Change-Id: I86773a3df7f249fae565bd15d8761a537a79651e
diff --git a/recipes-osmocom/libosmocore/libosmocore.inc b/recipes-osmocom/libosmocore/libosmocore.inc
index 5b21196..e5b34ae 100644
--- a/recipes-osmocom/libosmocore/libosmocore.inc
+++ b/recipes-osmocom/libosmocore/libosmocore.inc
@@ -2,10 +2,15 @@
 HOMEPAGE = "http://openbsc.gnumonks.org"
 LICENSE = "GPLv2+"
 
-INC_PR="r1.${META_TELEPHONY_OSMO_INC}"
+INC_PR="r2.${META_TELEPHONY_OSMO_INC}"
 
 LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"
 
 DEPENDS = "libtalloc gnutls lksctp-tools"
 
+PACKAGECONFIG ??= "\
+    libusb \
+    "
+PACKAGECONFIG[libusb] = "--enable-libusb,--disable-libusb,libusb,"
+
 inherit autotools pkgconfig