package/ell: needs headers >= 4.12

package/ell: needs headers >= 4.12

ell needs headers >= 4.12 since version 0.31 and
https://git.kernel.org/pub/scm/libs/ell/ell.git/commit?id=fa950995a48bbcd8f0d3dfbbe9a7f768aba5c50f

Indeed NLM_F_CAPPED, NLM_F_ACK_TLVS, NLMSGERR_ATTR_MSG and
NETLINK_EXT_ACK are only available since
https://github.com/torvalds/linux/commit/2d4bc93368f5a0ddb57c8c885cdad9c9b7a10ed5

So add this dependency to ell and its reverse dependencies

Fixes:
 - http://autobuild.buildroot.org/results/bafc0ee2a3bcb2418a3612da38eb9dcd586b57d4

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>