docs: networking: arcnet-hardware.rst: don't duplicate chapter names

Since changeset 58ad30cf91f0 ("docs: fix reference to core-api/namespaces.rst"),
auto-references for chapters are generated. This is a nice feature, but
has a drawback: no chapters can have the same sumber.

So, we need to change two chapter titles, to avoid warnings when
building the docs.

Fixes: 58ad30cf91f0 ("docs: fix reference to core-api/namespaces.rst")
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/arcnet-hardware.rst

···
 	11111           0xC400 (guessed - crashes tested system)
 	=============   ============================================
 
-CNet Technology Inc.
-====================
+CNet Technology Inc. (8-bit cards)
+==================================
 
 120 Series (8-bit cards)
 ------------------------
···
 parameters. These two jumpers are normally left open.
 
 
-CNet Technology Inc.
-====================
+CNet Technology Inc. (16-bit cards)
+===================================
 
 160 Series (16-bit cards)
 -------------------------