Fix with nettle >=4

Index: src/putty/sshaes.c
--- src/putty/sshaes.c.orig
+++ src/putty/sshaes.c
@@ -11,6 +11,7 @@
 #include <nettle/aes.h>
 #include <nettle/gcm.h>
 #include <nettle/memxor.h>
+#include <nettle/version.h>
 
 /*
  * Start by deciding whether we can support hardware AES at all.
@@ -313,7 +314,11 @@ static void aes128_gcm_mac_genresult(ssh2_mac *mac, un
 {
     struct AES128GCMContext *ctx = container_of(mac, struct AES128GCMContext, mac_if);
 
+#if NETTLE_VERSION_MAJOR > 3
+    nettle_gcm_aes128_digest(&ctx->ctx, blk);
+#else
     nettle_gcm_aes128_digest(&ctx->ctx, 16, blk);
+#endif
     increment_iv_step32(ctx->iv + 4, 2);
 }
 
@@ -455,7 +460,11 @@ static void aes256_gcm_mac_genresult(ssh2_mac *mac, un
 {
     struct AES256GCMContext *ctx = container_of(mac, struct AES256GCMContext, mac_if);
 
+#if NETTLE_VERSION_MAJOR > 3
+    nettle_gcm_aes256_digest(&ctx->ctx, blk);
+#else
     nettle_gcm_aes256_digest(&ctx->ctx, 16, blk);
+#endif
     increment_iv_step32(ctx->iv + 4, 2);
 }
 
