doc: Add mail address where it is missing

sys/include/embUnit.h

sys/shell/commands/sc_net_if.c

tests/unittests/main.c

tests/unittests/tests-core/tests-core-atomic.c

tests/unittests/tests-core/tests-core-bitarithm.c

tests/unittests/tests-core/tests-core-cib.c

tests/unittests/tests-core/tests-core-clist.c

tests/unittests/tests-core/tests-core-lifo.c

tests/unittests/tests-core/tests-core-priority-queue.c

tests/unittests/tests-core/tests-core.c

tests/unittests/tests-core/tests-core.h

tests/unittests/tests-netdev_dummy/tests-netdev_dummy.c

tests/unittests/tests-netdev_dummy/tests-netdev_dummy.h

tests/unittests/tests-nomac/tests-nomac.c

tests/unittests/tests-nomac/tests-nomac.h

tests/unittests/tests-pkt/tests-pkt.h

tests/unittests/tests-pktbuf/tests-pktbuf.h

tests/unittests/tests-pktqueue/tests-pktqueue.c

tests/unittests/tests-pktqueue/tests-pktqueue.h