bnxt_en: Check the FW_LLDP_AGENT flag before allowing DCBX host agent.

Check the additional flag in bnxt_hwrm_func_qcfg() before allowing
DCBX to be done in host mode.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>