bnxt_en: Restore MSIX after disabling SRIOV.

After SRIOV has been enabled and disabled, the MSIX vectors assigned to
the VFs have to be re-initialized.  Otherwise they cannot be re-used by
the PF.  For example, increasing the number of PF rings after disabling
SRIOV may fail if the PF uses MSIX vectors previously assigned to the VFs.

To fix this, we add logic in bnxt_restore_pf_fw_resources() to close the
NIC, clear and re-init MSIX, and re-open the NIC.

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