package/frr: drop libnl dependency

libnl is not needed to build frr since the addition of the package in
commit 26d82d006ba15777d19892b327bde343d82a9ff5

No mention of libnl found in https://github.com/FRRouting/frr or
https://docs.frrouting.org/projects/dev-guide/en/latest/building.html

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit efa955ac415e2b50f63710e4fc1de8fd3e0dc099)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/frr/Config.in

@@ -7,7 +7,6 @@ config BR2_PACKAGE_FRR
 	select BR2_PACKAGE_BASH
 	select BR2_PACKAGE_BUSYBOX_SHOW_OTHERS # bash
 	select BR2_PACKAGE_LIBYANG
-	select BR2_PACKAGE_LIBNL
 	select BR2_PACKAGE_READLINE
 	select BR2_PACKAGE_JSON_C
 	help

package/frr/frr.mk

@@ -12,7 +12,7 @@ FRR_CPE_ID_VENDOR = linuxfoundation
 FRR_CPE_ID_PRODUCT = free_range_routing
 FRR_AUTORECONF = YES
 
-FRR_DEPENDENCIES = host-frr readline json-c libyang libnl \
+FRR_DEPENDENCIES = host-frr readline json-c libyang \
 	$(if $(BR2_PACKAGE_C_ARES),c-ares)
 
 HOST_FRR_DEPENDENCIES = host-flex host-bison host-elfutils host-python3