net: 6lowpan: use array for find nhc id

This patch will remove the complete overengineered and overthinking rb data
structure for looking up the nhc by nhcid. Instead we using the existing
nhc next header array and iterate over it. It works now for 1 byte values
only. However there are only 1 byte nhc id values currently
supported and IANA also does not specify large than 1 byte values yet.
If there are 2 byte values for nhc ids specified we can revisit this
data structure and add support for it.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Reviewed-by: Stefan Schmidt <stefan@datenfreihafen.org>
Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Link: https://lore.kernel.org/r/20220428030534.3220410-3-aahringo@redhat.com
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 3029 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

6lowpan: add nhc module for GHC UDP detection

Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>