net: tcp: Do not overwrite remote address in new conn

When a new incoming connection is accepted, do not overwrite
the listening remote address. The remote address for the
listening socket is the any address (like :: for IPv6)
and not the accepted socket remote address.
This only affects the "net conn" shell command which prints
the remote address incorrectly. There is no problem accepting
new connections in this case.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>