cxgb4: Rename sched_class to avoid type clash

cxgb4: Rename sched_class to avoid type clash

drivers/net/ethernet/chelsio/cxgb4/sched.h declares a sched_class
struct which has a type name clash with struct sched_class
in kernel/sched/sched.h (a type used in a field in task_struct).

When cxgb4 is a builtin we end up with both sched_class types,
and as a result of this we wind up with DWARF (and derived from
that BTF) with a duplicate incorrect task_struct representation.
When cxgb4 is built-in this type clash can cause kernel builds to
fail as resolve_btfids will fail when confused which task_struct
to use. See [1] for more details.

As such, renaming sched_class to ch_sched_class (in line with
other structs like ch_sched_flowc) makes sense.

[1] https://lore.kernel.org/bpf/2412725b-916c-47bd-91c3-c2d57e3e6c7b@acm.org/

Reported-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Potnuri Bharat Teja <bharat@chelsio.com>
Link: https://patch.msgid.link/20251121181231.64337-1-alan.maguire@oracle.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>