bnxt_en: Poll link at the end of __bnxt_open_nic().

When shutting down the NIC, we shutdown async event processing before
freeing all the rings.  If there is a link change event during reset, the
driver may miss it and the link state may be incorrect after the NIC is
re-opened.  Poll the link at the end of __bnxt_open_nic() to get the
correct link status.

Signed-off-by Michael Chan <michael.chan@broadcom.com>

Signed-off-by: David S. Miller <davem@davemloft.net>