[build] remove unneeded-internal-declaration warning (#6040)
[build] remove unneeded-internal-declaration warning (#6040)

By inlining static functions defined in the header file.
srickardti/openthread,openthread/openthread,abtink/openthread,jwhui/openthread,srickardti/openthread,jwhui/openthread,openthread/openthread,jwhui/openthread,abtink/openthread,srickardti/openthread,srickardti/openthread,openthread/openthread,openthread/openthread,abtink/openthread,jwhui/openthread,abtink/openthread