selftests: net: use ip commands instead of teamd in team rx_mode test

selftests: net: use ip commands instead of teamd in team rx_mode test

Replace teamd daemon usage with ip link commands for team device
setup. teamd -d daemonizes and returns to the shell before port
addition completes, creating a race: the test may create the macvlan
(and check for its address on a slave) before teamd has finished
adding ports. This makes the test inherently dependent on scheduling
timing.

Using ip commands makes port addition synchronous, removing the race
and making the test deterministic.

Cc: Jiri Pirko <jiri@resnulli.us>
Cc: Jay Vosburgh <jv@jvosburgh.net>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260416185712.2155425-16-sdf@fomichev.me
Signed-off-by: Paolo Abeni <pabeni@redhat.com>