selftests: net: add team_bridge_macvlan rx_mode test

Add a test that exercises the ndo_change_rx_flags path through a
macvlan -> bridge -> team -> dummy stack. This triggers dev_uc_add
under addr_list_lock which flips promiscuity on the lower device.
With the new work queue approach, this must not deadlock.

Link: https://lore.kernel.org/netdev/20260214033859.43857-1-jiayuan.chen@linux.dev/
Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260416185712.2155425-15-sdf@fomichev.me
Signed-off-by: Paolo Abeni <pabeni@redhat.com>