6lowpan: Fix endianness issue in is_addr_link_local().

[ Upstream commit 9026c4927254f5bea695cc3ef2e255280e6a3011 ]

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>