netpoll: do not export netpoll_poll_[disable|enable]()

netpoll_poll_disable() and netpoll_poll_enable() are only used
from core networking code, there is no need to export them.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240820162053.3870927-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>