stream: group bool fields at tail of addrConnStream to reduce allocator size class

Four bool fields in addrConnStream were scattered among pointer- and
interface-sized fields, each forcing alignment padding before the next field:

  sentLast + receivedFirstMsg @ 96-97  6 B padding (before 8B-aligned pointer)
  decompressorSet             @ 160    7 B padding (before 16B-aligned interface)
  finished                    @ 248    7 B tail padding

Total: 20 B interior padding, 16 B net savings when all bools are moved to
the tail. addrConnStream shrinks from 256 B to 240 B, dropping from the
256 B to the 240 B allocator size class.

Fixes #9348

Author: gidotencate

stream.go

@@ -1498,19 +1498,28 @@ type addrConnStream struct {
 	callInfo         *callInfo
 	transport        transport.ClientTransport
 	ctx              context.Context
-	sentLast         bool
-	receivedFirstMsg bool
 	desc             *StreamDesc
 	codec            baseCodec
 	sendCompressorV0 Compressor
 	sendCompressorV1 encoding.Compressor
-	decompressorSet  bool
 	decompressorV0   Decompressor
 	decompressorV1   encoding.Compressor
 	parser           parser
 
 	// mu guards finished and is held for the entire finish method.
-	mu       sync.Mutex
+	mu sync.Mutex
+
+	// Bool fields are grouped at the tail to eliminate the alignment padding
+	// that would otherwise follow each bool when the next field is pointer- or
+	// int-sized. See https://github.com/grpc/grpc-go/issues/9348 for benchmarks.
+	// Add new bool fields here, not inline above.
+
+	// Not guarded by mu.
+	sentLast         bool
+	receivedFirstMsg bool
+	decompressorSet  bool
+
+	// Guarded by mu.
 	finished bool
 }