net: move ping to sys/net

* moved the former ping module from `sys` to `sys/net/link_layer` and renamed to l2_ping
* use defaulttransceiver instead of cc110x
* some refactoring
net: l2_ping uses radio_packet_t instead of packet_info_t
cpu/arm_common: c++: initial support for c++ added _kill (weak) and weak attribute for _kill_r
boards/msba2: provided c++ feature (cpp)
shell: introduced l2 ping shell commands
l2_ping: add to auto_init
Merge pull request #1495 from BytesGalore/EasyCppMixing_msba2_support_fix

cpu/arm_common C++ msba2 support fix
Merge pull request #1228 from OlegHahm/l2_ping

net: Link Layer Ping