package/connman: add missing libmnl dependency for nftables

package/connman: add missing libmnl dependency for nftables

Building with nftables support requires libmnl.

Fixes:
  - http://autobuild.buildroot.org/results/4afdacc0357eb3b86594757dd89623b6e5a5e362/
  - http://autobuild.buildroot.org/results/89e6f92dee4a93185891c48b5d7f7b5b0345b67e/
  - http://autobuild.buildroot.org/results/dd8a68827ca70838c59d82780cb3eadf6b9764c2/

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
[yann.morin.1998@free.fr: add autobuild referecnes]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>