selftests: netconsole: only restore MAC when it changed on resume

selftests: netconsole: only restore MAC when it changed on resume

The "mac" bind mode reactivation downs the interface, restores the saved
MAC and renames it to trigger a target resume. This assumes the recreated
interface comes back with a different MAC, which is true under
MACAddressPolicy=none (as on the Netdev CI) but not when MACs are
persistent. In the persistent case netconsole resumes the target on its
own, and the down/restore/rename flow instead drops it and fails the test.

Guard the block on the MAC having actually changed so the test passes
under both policies.

Fixes: 6ecc08329bab ("selftests: netconsole: validate target resume")
Reported-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Closes: https://lore.kernel.org/netdev/f398373e-2cb4-4649-a491-9763df94d98b@kernel.org/
Signed-off-by: Andre Carvalho <asantostc@gmail.com>
Tested-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260710-netcons-mac-reload-v1-1-3fb1bcc70b4a@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>