BUG/MEDIUM: servers: fix typo "src" instead of "srv"

When copying the settings for all servers when using server templates,
fix a typo, or we would never copy the length of the ALPN to be used for
checks.

This should be backported to 1.9.
diff --git a/src/server.c b/src/server.c
index 12a14ad..9916361 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1639,7 +1639,7 @@
 	srv->check.port               = src->check.port;
 	srv->check.sni                = src->check.sni;
 	srv->check.alpn_str           = src->check.alpn_str;
-	srv->check.alpn_len           = srv->check.alpn_len;
+	srv->check.alpn_len           = src->check.alpn_len;
 	/* Note: 'flags' field has potentially been already initialized. */
 	srv->flags                   |= src->flags;
 	srv->do_check                 = src->do_check;