fixup: introduce input_buffer_factory concept.

Signed-off-by: Radoslaw Zarzynski <[email protected]>

src/net/posix-stack.cc

@@ -327,9 +327,6 @@ future<temporary_buffer<char>>
 posix_data_source_impl::get() {
     _buf = _buffer_factory->create(_buffer_allocator);
     return _fd->read_some(_buf.get_write(), _buf.size()).then([this] (size_t size) {
-        // XXX: if the next v2 frame's prologue isn't available yet, size will be
-        // smaller than the estimation and extra get() would be necessary. I hope
-        // this won't the typical case.
         _buf.trim(size);
         auto ret = std::move(_buf);
         return make_ready_future<temporary_buffer<char>>(std::move(ret));