Merge pull request #12844 from apolcyn/backport_ruby_gc_rooted_bugs

Backport ruby non-GC-rooted variable fixes to 1.6.x
diff --git a/src/ruby/ext/grpc/rb_call.c b/src/ruby/ext/grpc/rb_call.c
index 5550bb7..29c4a94 100644
--- a/src/ruby/ext/grpc/rb_call.c
+++ b/src/ruby/ext/grpc/rb_call.c
@@ -101,6 +101,7 @@
     return;
   }
   destroy_call((grpc_rb_call *)p);
+  xfree(p);
 }
 
 static size_t md_ary_datasize(const void *p) {