net/i40e: fix DCB initialization

Stopping LLDP is necessary for DPDK, but it will cause DCB init failure.
For kernel shared code, the prerequisite for successful initialization
of DCB is that LLDP is enabled. This patch starts LLDP before DCB init
and stops it when init finishes.

Fixes: a8e84b22bd55 ("net/i40e/base: support persistent LLDP")
Cc: stable@dpdk.org
Signed-off-by: Shougang Wang <shougangx.wang@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>
Acked-by: Xiaolong Ye <xiaolong.ye@intel.com>