[Fix] Fix allocation of the control buffer

[Fix] Fix allocation of the control buffer

* Refactored rspamd_control_fill_msghdr to accept
  a caller-provided control buffer, fixing the
  lifetime bug where a pointer to a local array
  was stored in msg_control.
* Replaced static buffers with automatic (stack)
  buffers at the exact call sites of sendmsg/recvmsg,
  so PowerPC and similar platforms won’t choke on
  non-constant expressions.

Issue: #5637