docs: remove obsolete description about threaded NAPI

Commit 2677010 ("Add support to set NAPI threaded for individual
NAPI") introduced threaded NAPI configuration per individual NAPI
instance, however obsolete description that threaded NAPI is per device
has remained.

Remove the old description and clarify that only NAPI instances running
in threaded mode spawn kernel threads by changing "Each NAPI instance"
to "Each threaded NAPI instance".

Signed-off-by: Kohei Enju <[email protected]>
Reviewed-by: Samiullah Khawaja <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: hyperenju

Documentation/networking/napi.rst

@@ -433,9 +433,8 @@ Threaded NAPI
 
 Threaded NAPI is an operating mode that uses dedicated kernel
 threads rather than software IRQ context for NAPI processing.
-The configuration is per netdevice and will affect all
-NAPI instances of that device. Each NAPI instance will spawn a separate
-thread (called ``napi/${ifc-name}-${napi-id}``).
+Each threaded NAPI instance will spawn a separate thread
+(called ``napi/${ifc-name}-${napi-id}``).
 
 It is recommended to pin each kernel thread to a single CPU, the same
 CPU as the CPU which services the interrupt. Note that the mapping