bnxt_en: Improve device shutdown method.

Especially when bnxt_shutdown() is called during kexec, we need to
disable MSIX and disable Bus Master to completely quiesce the device.
Make these 2 calls unconditionally in the shutdown method.

Fixes: c20dc142 ("bnxt_en: Disable bus master during PCI shutdown and driver unload.")
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>