[SQUASH ME] c++: sys: add extern C in header files (`./net/ccn_lite/*.h` && `./net/ccn_lite/util/*.h`)

[SQUASH ME] c++: sys: add extern C in header files (`./net/ccn_lite/*/*.h`)
[SQUASH ME] c++: sys: add extern C in header files (`./net/network_layer/sixlowpan/*/*.h`)
[SQUASH ME] c++: sys: add extern C in header files (`./net/network_layer/routing/rpl/*.h`)
[SQUASH ME] c++: sys: add extern C in header files (`./net/transport_layer/*/*.h`)
[SQUASH ME] c++: sys: add extern C in header files (`./net/oneway-malloc/include/malloc.h`)
[SQUASH ME] c++: sys: add extern C in header files (`./posix/*/*/*.h`)