BUILD: connection: silence gcc warning with extra parentheses

Commit 8a4ffa0a ("MINOR: send-proxy-v2: sends authority TLV according
to TLV received") is missing parentheses around a variable assignment
used as condition in an if statement, and gcc isn't happy about it.
diff --git a/src/connection.c b/src/connection.c
index 33f3b22..9122850 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -1316,7 +1316,7 @@
 		}
 #ifdef USE_OPENSSL
 		else {
-			if (value = ssl_sock_get_sni(remote))
+			if ((value = ssl_sock_get_sni(remote)))
 				value_len = strlen(value);
 		}
 #endif