env/dpdk: add rte_net dependency to vhost

rte_net is a dependency for both rte_vhost and rte_power.

Next patch will simplify the checks to include rte_power,
and keeping this depenency next to component that directly
depends on it will make it easier to understand.

Since DPDK_LIB_LIST is sorted by the end of the env.mk,
it shouldn't be a problem to include the rte_net twice.

Signed-off-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Change-Id: If2bb2aa5d972148ca8143023657b0aec45306a08
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/12991


Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>