Add ByteBufUtils.writeUint{8,16,32,64}

Plain ByteBufUtils.write() methods are hiding the width argument,
hence can potentially break binary encodings on type change.

Add explicit methods, so that the intent is documented and actually
breaks when incorrect type is applied.

Change-Id: I26e14048b4d4d44ea5044ff852650b18ca90012f
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>