tests: fix doxygen grouping

tests/driver_kw2xrf/kw2xrf_params.h

tests/fault_handler/main.c

tests/gnrc_sock_ip/constants.h

tests/gnrc_sock_ip/main.c

tests/gnrc_sock_ip/stack.h

tests/gnrc_sock_udp/constants.h

tests/gnrc_sock_udp/stack.c

tests/gnrc_sock_udp/stack.h

tests/lwip_sock_ip/constants.h

tests/lwip_sock_ip/main.c

tests/lwip_sock_ip/stack.c

tests/lwip_sock_ip/stack.h

tests/lwip_sock_tcp/constants.h

tests/lwip_sock_tcp/stack.c

tests/lwip_sock_tcp/stack.h

tests/lwip_sock_udp/constants.h

tests/lwip_sock_udp/stack.c

tests/lwip_sock_udp/stack.h

tests/minimal/main.c

tests/pkg_cayenne-lpp/main.c