Merge pull request #5038 from cgundogan/pr/pktdump/global_pid

examples/default/main.c

examples/gnrc_networking/udp.c

sys/include/net/gnrc/pktdump.h

sys/net/gnrc/pktdump/gnrc_pktdump.c

tests/driver_at86rf2xx/main.c

tests/driver_kw2xrf/main.c

tests/driver_nrfmin/main.c

tests/driver_xbee/main.c

tests/slip/main.c

tests/zep/main.c