build: request libnl-route-3 and version 3.2.19

Because libteam uses functions from libnl-route-3 (such as
rtnl_link_add), it should also search for this library with pkgconfig,
include its flags, and so on. Additionally, version 3.2.19 is required
due to the use of, for example, rtnl_link_set_carrier.

Signed-off-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>