net: ipv6: rpl*: Fix strange kerneldoc warnings due to bad header

net/ipv6/rpl_iptunnel.c:15: warning: cannot understand function prototype: 'struct rpl_iptunnel_encap '

The header on the file containing the author copyright message uses
kerneldoc /** opener. This confuses the parser when it gets to

struct rpl_iptunnel_encap {
	struct ipv6_rpl_sr_hdr srh[0];
};

Similarly:

net//ipv6/rpl.c:10: warning: Function parameter or member 'x' not described in 'IPV6_PFXTAIL_LEN'

where IPV6_PFXTAIL_LEN is a macro definition, not a function.

Convert the header comments to a plain /* comment.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20201028013123.931816-1-andrew@lunn.chSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/rpl.c

 // SPDX-License-Identifier: GPL-2.0-only
-/**
+/*
  * Authors:
  * (C) 2020 Alexander Aring <alex.aring@gmail.com>
  */

net/ipv6/rpl_iptunnel.c

 // SPDX-License-Identifier: GPL-2.0-only
-/**
+/*
  * Authors:
  * (C) 2020 Alexander Aring <alex.aring@gmail.com>
  */