[alts] Update max concurrent streams to ALTS handshaker service to 100. (#37966)

This matches the gRPC-Go behavior.

Closes #37966

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/37966 from matthewstevenson88:max-concurrent-streams 8395f097e4
PiperOrigin-RevId: 688180702

src/core/tsi/alts/handshaker/alts_handshaker_client.cc

@@ -929,11 +929,11 @@ void alts_handshaker_client_destroy(alts_handshaker_client* c) {
 }
 
 size_t MaxNumberOfConcurrentHandshakes() {
-  size_t max_concurrent_handshakes = 40;
+  size_t max_concurrent_handshakes = 100;
   absl::optional<std::string> env_var_max_concurrent_handshakes =
       grpc_core::GetEnv(kMaxConcurrentStreamsEnvironmentVariable);
   if (env_var_max_concurrent_handshakes.has_value()) {
-    size_t effective_max_concurrent_handshakes = 40;
+    size_t effective_max_concurrent_handshakes = 100;
     if (absl::SimpleAtoi(*env_var_max_concurrent_handshakes,
                          &effective_max_concurrent_handshakes)) {
       max_concurrent_handshakes = effective_max_concurrent_handshakes;

test/core/tsi/alts/handshaker/alts_handshaker_client_test.cc

@@ -512,17 +512,17 @@ TEST(AltsHandshakerClientTest, ScheduleRequestGrpcCallFailureTest) {
 
 TEST(MaxNumberOfConcurrentHandshakesTest, Default) {
   grpc_core::UnsetEnv(kMaxConcurrentStreamsEnvironmentVariable);
-  EXPECT_EQ(MaxNumberOfConcurrentHandshakes(), 40);
+  EXPECT_EQ(MaxNumberOfConcurrentHandshakes(), 100);
 }
 
 TEST(MaxNumberOfConcurrentHandshakesTest, EnvVarNotInt) {
   grpc_core::SetEnv(kMaxConcurrentStreamsEnvironmentVariable, "not-a-number");
-  EXPECT_EQ(MaxNumberOfConcurrentHandshakes(), 40);
+  EXPECT_EQ(MaxNumberOfConcurrentHandshakes(), 100);
 }
 
 TEST(MaxNumberOfConcurrentHandshakesTest, EnvVarNegative) {
   grpc_core::SetEnv(kMaxConcurrentStreamsEnvironmentVariable, "-10");
-  EXPECT_EQ(MaxNumberOfConcurrentHandshakes(), 40);
+  EXPECT_EQ(MaxNumberOfConcurrentHandshakes(), 100);
 }
 
 TEST(MaxNumberOfConcurrentHandshakesTest, EnvVarSuccess) {