kobject: reduce uevent_sock_mutex scope

kobject: reduce uevent_sock_mutex scope

This is a followup of commit a3498436b3a0 ("netns: restrict uevents")

- uevent_sock_mutex no longer protects uevent_seqnum thanks
  to prior patch in the series.

- uevent_net_broadcast() can run without holding uevent_sock_mutex.

- Instead of grabbing uevent_sock_mutex before calling
  kobject_uevent_net_broadcast(), we can move the
  mutex_lock(&uevent_sock_mutex) to the place we iterate over
  uevent_sock_list : uevent_net_broadcast_untagged().

After this patch, typical netdevice creations and destructions
calling uevent_net_broadcast_tagged() no longer need to acquire
uevent_sock_mutex.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Christian Brauner <brauner@kernel.org>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20240214084829.684541-3-edumazet@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>