mlxsw: spectrum_router: Rename two functions

mlxsw: spectrum_router: Rename two functions

The function mlxsw_sp_nexthop_counter_alloc() doesn't directly allocate
anything, and mlxsw_sp_nexthop_counter_free() doesn't directly free. For
the following patches, we will need names for functions that actually do
those things. Therefore rename to mlxsw_sp_nexthop_counter_enable() and
mlxsw_sp_nexthop_counter_disable() to free up the namespace.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/f59272958697a718f090f59f892d32beabcd8972.1709901020.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>