Add documentation for ACD timeout variable as it was missing.

Signed-off-by: Jukka Rissanen <[email protected]>

The net_if.c:rs_timeout() is sending a new IPv6 router solicitation
message to network by calling net_if_start_rs(). That function will
then acquire iface->lock and call net_ipv6_start_rs() which will try
to send the RS message and acquire TX send lock.
During this RS send, we might receive TCP data that could try to
send an ack to peer. This will then in turn cause also TX lock
to be acquired. Depending on timing, the lock ordering between
rx thread and system workq might mix which could lead to deadlock.
Fix this issue by releasing the iface->lock before starting the
RS sending process. The net_if_start_rs() does not really need to
keep the interface lock for a long time as it is the only one sending
the RS message.

Fixes zephyrproject-rtos#86499

Signed-off-by: Jukka Rissanen <[email protected]>

In order to avoid any mutex deadlocks between iface->lock and
TX lock, release the interface lock before calling a function
that will acquire TX lock. See previous commit for similar issue
in RS timer handling.

Signed-off-by: Jukka Rissanen <[email protected]>

In order to avoid any mutex deadlocks between iface->lock and
TX lock, release the interface lock before calling a function
that will acquire TX lock. See previous commit for similar issue
in RS timer handling. So here we create a separate list of ACD
addresses that are to be started when network interface comes up
without iface->lock held.

Signed-off-by: Jukka Rissanen <[email protected]>