bnxt_en: implement devlink dev reload driver_reinit

The RTNL lock must be held between down and up to prevent interleaving
state changes, especially since external state changes might release
and allocate different driver resource subsets that would otherwise
need to be tracked and carefully handled. If the down function fails,
then devlink will not call the corresponding up function, thus the
lock is released in the down error paths.

v2: Don't use devlink_reload_disable() and devlink_reload_enable().
Instead, check that the netdev is not in unregistered state before
proceeding with reload.

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