[#3388] Fix licencing issue for test files sflphone-common

sflphone-common/test/accounttest.cpp

sflphone-common/test/accounttest.h

sflphone-common/test/audiolayertest.cpp

sflphone-common/test/audiolayertest.h

sflphone-common/test/configurationtest.cpp

sflphone-common/test/configurationtest.h

sflphone-common/test/constants.h

sflphone-common/test/historytest.cpp

sflphone-common/test/historytest.h

sflphone-common/test/hookmanagertest.cpp

sflphone-common/test/hookmanagertest.h

sflphone-common/test/main.cpp

sflphone-common/test/mainbuffertest.cpp

sflphone-common/test/mainbuffertest.h

sflphone-common/test/numbercleanertest.cpp

sflphone-common/test/numbercleanertest.h

sflphone-common/test/pluginmanagertest.cpp

sflphone-common/test/pluginmanagertest.h

sflphone-common/test/rtptest.cpp

sflphone-common/test/rtptest.h