dev: Pass netdevice_tracker to dev_get_by_flags_rcu().

dev: Pass netdevice_tracker to dev_get_by_flags_rcu().

This is a follow-up for commit eb1ac9ff6c4a5 ("ipv6: anycast: Don't
hold RTNL for IPV6_JOIN_ANYCAST.").

We should not add a new device lookup API without netdevice_tracker.

Let's pass netdevice_tracker to dev_get_by_flags_rcu() and rename it
with netdev_ prefix to match other newer APIs.

Note that we always use GFP_ATOMIC for netdev_hold() as it's expected
to be called under RCU.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/netdev/20250708184053.102109f6@kernel.org/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250711051120.2866855-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>