selftests: net: lib: Rename ip_link_master() to ip_link_set_master()

Let's have a verb in that function name to make it clearer what's going on.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/fbf7c53a429b340b9cff5831280ea8c305a224f9.1733412063.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>