Fail to transmit whole resource value in notification message if it r…

[anttiylitokola]

…equires blockwise transfer

• Fixes error reported in https://github.com/ARMmbed/mbed-client/issues/481

[TeroJaasko]

Please rebase this branch with master before merging to get cleaner history, preferably also squash 0120090b9d2 to 44554382299e.