CVE-2026-98966: bonding: fix the program leak when XDP is replaced

In the Linux kernel, the following vulnerability has been resolved:

bonding: fix the program leak when XDP is replaced

We need to release the reference on the old BPF prog, whether we are going to no-prog, or replacing the prog with another.

Spotted by AI while running tests for the propagation series (leaked programs were accumulating). Selftest will come in the net-next series to avoid conflicts.