network: Factorize netlink creation and verification
network: Factorize netlink creation and verification

A lot of code was duplicated between the different types of netlink
links. This patch takes care of the factorization.

Signed-off-by: Sebastien Boeuf <90b401417360b1924ef3f520ddee932686110f85@intel.com>

containers/virtcontainers,wcwxyz/virtcontainers,containers/virtcontainers,wcwxyz/virtcontainers,wcwxyz/virtcontainers