cmd/tailscale: change formatting of "tailscale status"

* show DNS name over hostname, removing domain's common MagicDNS suffix.
  only show hostname if there's no DNS name.
  but still show shared devices' MagicDNS FQDN.

* remove nerdy low-level details by default: endpoints, DERP relay,
  public key.  They're available in JSON mode still for those who need
  them.

* only show endpoint or DERP relay when it's active with the goal of
  making debugging easier. (so it's easier for users to understand
  what's happening) The asterisks are gone.

* remove Tx/Rx numbers by default for idle peers; only show them when
  there's traffic.

* include peers' owner login names

* add CLI option to not show peers (matching --self=true, --peers= also
  defaults to true)

* sort by DNS/host name, not public key

* reorder columns

ipn/ipnstate/ipnstate.go

@@ -25,9 +25,10 @@ import (
 
 // Status represents the entire state of the IPN network.
 type Status struct {
-	BackendState string
-	TailscaleIPs []netaddr.IP // Tailscale IP(s) assigned to this node
-	Self         *PeerStatus
+	BackendState   string
+	TailscaleIPs   []netaddr.IP // Tailscale IP(s) assigned to this node
+	Self           *PeerStatus
+	MagicDNSSuffix string // e.g. "userfoo.tailscale.net" (no surrounding dots)
 
 	Peer map[key.Public]*PeerStatus
 	User map[tailcfg.UserID]tailcfg.UserProfile
@@ -103,6 +104,12 @@ func (sb *StatusBuilder) SetBackendState(v string) {
 	sb.st.BackendState = v
 }
 
+func (sb *StatusBuilder) SetMagicDNSSuffix(v string) {
+	sb.mu.Lock()
+	defer sb.mu.Unlock()
+	sb.st.MagicDNSSuffix = v
+}
+
 func (sb *StatusBuilder) Status() *Status {
 	sb.mu.Lock()
 	defer sb.mu.Unlock()