Fix test for in-place encryption using GCM

We used to skip the test that encryption is done in place for GCM.
It turns out we were simply passing too small a buffer.  Use
a larger buffer, and reenable the test.

srtp_test.go

@@ -307,19 +307,19 @@ func testRTPLifecyleInPlace(t *testing.T, profile ProtectionProfile) {
 		}
 
 		// Copy packet, asserts that everything was done in place
-		encryptInput := make([]byte, len(decryptedRaw), len(decryptedRaw)+10)
+		slack := 10
+		if profile == profileGCM {
+			slack = 16
+		}
+		encryptInput := make([]byte, len(decryptedRaw), len(decryptedRaw)+slack)
 		copy(encryptInput, decryptedRaw)
 
 		actualEncrypted, err := encryptContext.EncryptRTP(encryptInput, encryptInput, encryptHeader)
 		switch {
 		case err != nil:
 			t.Fatal(err)
 		case &encryptInput[0] != &actualEncrypted[0]:
-			if profile == profileCTR {
-				t.Errorf("EncryptRTP failed to encrypt in place")
-			} else {
-				t.Logf("Ignoring failure on GCM run")
-			}
+			t.Errorf("EncryptRTP failed to encrypt in place")
 		case encryptHeader.SequenceNumber != testCase.sequenceNumber:
 			t.Errorf("EncryptRTP failed to populate input rtp.Header")
 		}
@@ -378,19 +378,19 @@ func testRTPReplayProtection(t *testing.T, profile ProtectionProfile) {
 		}
 
 		// Copy packet, asserts that everything was done in place
-		encryptInput := make([]byte, len(decryptedRaw), len(decryptedRaw)+10)
+		slack := 10
+		if profile == profileGCM {
+			slack = 16
+		}
+		encryptInput := make([]byte, len(decryptedRaw), len(decryptedRaw)+slack)
 		copy(encryptInput, decryptedRaw)
 
 		actualEncrypted, err := encryptContext.EncryptRTP(encryptInput, encryptInput, encryptHeader)
 		switch {
 		case err != nil:
 			t.Fatal(err)
 		case &encryptInput[0] != &actualEncrypted[0]:
-			if profile == profileCTR {
-				t.Errorf("EncryptRTP failed to encrypt in place")
-			} else {
-				t.Logf("Ignoring failure on GCM run")
-			}
+			t.Errorf("EncryptRTP failed to encrypt in place")
 		case encryptHeader.SequenceNumber != testCase.sequenceNumber:
 			t.Fatal("EncryptRTP failed to populate input rtp.Header")
 		}