net: netdevsim: fix nsim_pp_hold_write()

nsim_pp_hold_write() has two problems:

1) It may return with rtnl held, as found by syzbot.

2) Its return value does not propagate an error if any.

Fixes: 1580cbcb ("net: netdevsim: add some fake page pool use")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241216083703.1859921-1-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>