bnxt_en: Add BNXT_STATE_IN_FW_RESET state.

The new flag will be set in subsequent patches when firmware is
going through reset.  If bnxt_close() is called while the new flag
is set, the FW reset sequence will have to be aborted because the
NIC is prematurely closed before FW reset has completed.  We also
reject SRIOV configurations while FW reset is in progress.

v2: No longer drop rtnl_lock() in close and wait for FW reset to complete.

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