net: bonding: Add SPDX identifier to remaining files

Previous batches of SPDX conversion missed bond_main.c and bonding_priv.h
because these files doesn't mention intended GPL version. Add SPDX identifier
to these files, assuming GPL 1.0+.

Cc: Thomas Davis <[e-mail]>
Cc: Christophe JAILLET <[e-mail]>
Cc: Stephen Hemminger <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: Bagas Sanjaya <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

drivers/net/bonding/bond_main.c

···
+// SPDX-License-Identifier: GPL-1.0+
 /*
  * originally based on the dummy device.
  *
  * Copyright 1999, Thomas Davis, [e-mail].
- * Licensed under the GPL. Based on dummy.c, and eql.c devices.
+ * Based on dummy.c, and eql.c devices.
  *
  * bonding.c: an Ethernet Bonding driver
  *

drivers/net/bonding/bonding_priv.h

···
+/* SPDX-License-Identifier: GPL-1.0+ */
 /*
  * Bond several ethernet interfaces into a Cisco, running 'Etherchannel'.
  *
···
  *
  * BUT, I'm the one who modified it for ethernet, so:
  * (c) Copyright 1999, Thomas Davis, [e-mail]
- *
- *	This software may be used and distributed according to the terms
- *	of the GNU Public License, incorporated herein by reference.
  *
  */
 

include/net/bonding.h

···
+/* SPDX-License-Identifier: GPL-1.0+ */
 /*
  * Bond several ethernet interfaces into a Cisco, running 'Etherchannel'.
  *
···
  *
  * BUT, I'm the one who modified it for ethernet, so:
  * (c) Copyright 1999, Thomas Davis, [e-mail]
- *
- *	This software may be used and distributed according to the terms
- *	of the GNU Public License, incorporated herein by reference.
  *
  */