net: hsr: constify hsr_ops and prp_ops protocol operation structures

net: hsr: constify hsr_ops and prp_ops protocol operation structures

The hsr_ops and prp_ops structures are assigned to hsr->proto_ops during
device initialization and are never modified at runtime. Declaring them
as const allows the compiler to place these structures in read-only
memory, which improves security by preventing accidental or malicious
modification of the function pointers they contain.

The proto_ops field in struct hsr_priv is also updated to a const
pointer to maintain type consistency.

Signed-off-by: Luka Gejak <luka.gejak@linux.dev>
Reviewed-by: Felix Maurer <fmaurer@redhat.com>
Link: https://patch.msgid.link/20260326174600.136232-2-luka.gejak@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>