Use accessors instead of reaching into DH to fix build with opaque DH
in LibreSSL 3.5

Index: src/apps/relay/mainrelay.c
--- src/apps/relay/mainrelay.c.orig
+++ src/apps/relay/mainrelay.c
@@ -2710,7 +2710,7 @@ static DH *get_dh566(void) {
 
 	if ((dh = DH_new()) == NULL )
 		return (NULL );
-#if OPENSSL_VERSION_NUMBER < 0x10100000L
+#if OPENSSL_VERSION_NUMBER < 0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
 	dh->p = BN_bin2bn(dh566_p, sizeof(dh566_p), NULL );
 	dh->g = BN_bin2bn(dh566_g, sizeof(dh566_g), NULL );
 	if ((dh->p == NULL )|| (dh->g == NULL)){ DH_free(dh); return(NULL);}
@@ -2748,7 +2748,7 @@ static DH *get_dh1066(void) {
 
 	if ((dh = DH_new()) == NULL )
 		return (NULL );
-#if OPENSSL_VERSION_NUMBER < 0x10100000L
+#if OPENSSL_VERSION_NUMBER < 0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
 	dh->p = BN_bin2bn(dh1066_p, sizeof(dh1066_p), NULL );
 	dh->g = BN_bin2bn(dh1066_g, sizeof(dh1066_g), NULL );
 	if ((dh->p == NULL )|| (dh->g == NULL)){ DH_free(dh); return(NULL);}
@@ -2799,7 +2799,7 @@ static DH *get_dh2066(void) {
 
 	if ((dh = DH_new()) == NULL )
 		return (NULL );
-#if OPENSSL_VERSION_NUMBER < 0x10100000L
+#if OPENSSL_VERSION_NUMBER < 0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
 	dh->p = BN_bin2bn(dh2066_p, sizeof(dh2066_p), NULL );
 	dh->g = BN_bin2bn(dh2066_g, sizeof(dh2066_g), NULL );
 	if ((dh->p == NULL )|| (dh->g == NULL)){ DH_free(dh); return(NULL);}