babeld: free blob-buffers that are on stack

babeld: free blob-buffers that are on stack

As Felix mentioned:
If a buffer was already allocated, blob_buf_init reuses it. You can
keep reusing it as many times as you want. You only need to call
blob_buf_free if you explicitly want to free the buffer memory
(e.g. on exit, or if the blob_buf is on stack).

http://lists.openwrt.org/pipermail/openwrt-devel/2021-October/036722.html

This PR frees the blob-buffers that are on the stack.

Signed-off-by: Nick Hainke <vincent@systemli.org>