sys: random: rename genrand_* to random_*

drivers/ethos/ethos.c

sys/auto_init/auto_init.c

sys/include/random.h

sys/net/gnrc/application_layer/tftp/gnrc_tftp.c

sys/net/gnrc/application_layer/zep/gnrc_zep.c

sys/net/gnrc/network_layer/ndp/gnrc_ndp.c

sys/net/gnrc/network_layer/ndp/host/gnrc_ndp_host.c

sys/net/gnrc/network_layer/ndp/internal/gnrc_ndp_internal.c

sys/net/gnrc/network_layer/ndp/router/gnrc_ndp_router.c

sys/net/gnrc/network_layer/sixlowpan/nd/gnrc_sixlowpan_nd.c

sys/posix/sockets/posix_sockets.c

sys/random/mersenne.c

sys/random/minstd.c

sys/random/musl_lcg.c

sys/random/prng_tinymt32.c

sys/shell/commands/sc_random.c

tests/bloom_bytes/main.c

tests/pthread_barrier/main.c

tests/pthread_rwlock/main.c