wpan: rework bluetooth / wpan and 6lowpan dependencies

- remove/rename of 6lowpan-iphc
upstream change in 3.17: 6lowpan: introduce new net/6lowpan directory
id: 2c6bed7cfcd3f594ed9e4d6919fa2ebea2243d19

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>

SVN-Revision: 45529