[#2485] Use RecvByteBufAllocator for all allocations related to read from Channel

Motivation:
At the moment we sometimes use only RecvByteBufAllocator.guess() to guess the next size and the use the ByteBufAllocator.* directly to allocate the buffer. We should always use RecvByteBufAllocator.allocate(...) all the time as this makes the behavior easier to adjust.

Modifications:
Change the read() implementations to make use of RecvByteBufAllocator.

Result:
Behavior is more consistent.