all: fix typos where we repeat repeat ourselves

Found with the regex `\b([A-Za-z]+) \1\b`.

Updates #cleanup

Change-Id: I4cc51784d9b6437d3d0c66b531828707f87f7fd5
Signed-off-by: Alex Chan <alexc@tailscale.com>

net/dns/resolver/forwarder.go

@@ -1349,8 +1349,7 @@ func (f *forwarder) forwardWithDestChan(ctx context.Context, query packet, respo
 
 			// If we haven't got an error or a successful response,
 			// include all resolvers in the error message so we can
-			// at least see what what servers we're trying to
-			// query.
+			// at least see what servers we're trying to query.
 			var resolverAddrs []string
 			for _, rr := range resolvers {
 				resolverAddrs = append(resolverAddrs, rr.name.Addr)

net/netmon/netmon.go

@@ -267,7 +267,7 @@ func (cd *ChangeDelta) AnyInterfaceUp() bool {
 
 // isInterestingInterfaceChange reports whether any interfaces have changed in a meaningful way.
 // This excludes interfaces that are not interesting per IsInterestingInterface and
-// filters out changes to interface IPs that that are uninteresting (e.g. link-local addresses).
+// filters out changes to interface IPs that are uninteresting (e.g. link-local addresses).
 func (cd *ChangeDelta) isInterestingInterfaceChange() bool {
 	// If there is no old state, everything is considered changed.
 	if cd.old == nil {

net/packet/header.go

@@ -45,7 +45,7 @@ type HeaderChecksummer interface {
 	Header
 
 	// WriteCheck writes the correct checksum into buf, which should
-	// be be the already-marshalled header and payload.
+	// be the already-marshalled header and payload.
 	WriteChecksum(buf []byte)
 }