The netmap.NetworkMap type is deprecated and going away, and
reconfigAppConnectorLocked only needed its SelfNode field anyway.
Take a tailcfg.NodeView instead and check its validity in place of
the old nil netmap check.
Updates #12542
Change-Id: Id617845b67416404500cca438ce4ac0372cd8a8e
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>