ipn/ipnlocal: exclude mullvad exit nodes from TailFS peers list

This is a temporary solution to at least omit Mullvad exit nodes
from the list of TailFS peers. Once we can identify peers that are
actually sharing via TailFS, we can remove this, but for alpha it'll
be sufficient to just omit Mullvad.

Updates tailscale/corp#17766

Signed-off-by: Percy Wegmann <percy@tailscale.com>

Author: oxtoacart

ipn/ipnlocal/tailfs.go

@@ -238,6 +238,13 @@ func (b *LocalBackend) updateTailFSPeersLocked(nm *netmap.NetworkMap) {
 
 	tailfsRemotes := make([]*tailfs.Remote, 0, len(nm.Peers))
 	for _, p := range nm.Peers {
+		// Exclude mullvad exit nodes from list of TailFS peers
+		// TODO(oxtoacart) - once we have a better mechanism for finding only accessible sharers
+		// (see below) we can remove this logic.
+		if strings.HasSuffix(p.Name(), ".mullvad.ts.net.") {
+			continue
+		}
+
 		peerID := p.ID()
 		url := fmt.Sprintf("%s/%s", peerAPIBase(nm, p), tailFSPrefix[1:])
 		tailfsRemotes = append(tailfsRemotes, &tailfs.Remote{