xen/netfront: Comment Correction: Fix Spelling Error and Description of Queue Quantity Rules

The original comments contained spelling errors and incomplete logical
descriptions, which could easily lead to misunderstandings of the code
logic. The specific modifications are as follows:

Correct the spelling error by changing "inut max" to "but not exceed the
maximum limit";

Add the note "If the user has not specified a value, the default maximum
limit is 8" to clarify the default value logic;

Improve the coherence of the statement to make the queue quantity rules
clearer.

After the modification, the comments can accurately reflect the code
behavior of "taking the smaller value between the number of CPUs and the
default maximum limit of 8 for the number of queues", enhancing code
maintainability.

Signed-off-by: Chu Guangqing <chuguangqing@inspur.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://patch.msgid.link/20251103032212.2462-1-chuguangqing@inspur.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>