6lowpan: nuke net_ieee802154_lowpan() accessor when 6lowpan is disabled

6lowpan: nuke net_ieee802154_lowpan() accessor when 6lowpan is disabled

Johannes noted this is not needed, all of the fragment
accessors don't need CONFIG_NET_NS. This goes test compiled with
CONFIG_BT_6LOWPAN=y and a disabled CONFIG_NET_NS.

CC: Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Cc: linux-zigbee-devel@lists.sourceforge.net
Cc: David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>