qerror: Clean up QERR_ macros to expand into a single string

These macros expand into error class enumeration constant, comma,
string.  Unclean.  Has been that way since commit 13f59ae.

The error class is always ERROR_CLASS_GENERIC_ERROR since the previous
commit.

Clean up as follows:

* Prepend every use of a QERR_ macro by ERROR_CLASS_GENERIC_ERROR, and
  delete it from the QERR_ macro.  No change after preprocessing.

* Rewrite error_set(ERROR_CLASS_GENERIC_ERROR, ...) into
  error_setg(...).  Again, no change after preprocessing.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/net/net.c b/net/net.c
index 7b5f519..7793366 100644
--- a/net/net.c
+++ b/net/net.c
@@ -945,16 +945,16 @@
             break;
 
         default:
-            error_set(errp, QERR_INVALID_PARAMETER_VALUE, "type",
-                      "a netdev backend type");
+            error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "type",
+                       "a netdev backend type");
             return -1;
         }
     } else {
         u.net = object;
         opts = u.net->opts;
         if (opts->kind == NET_CLIENT_OPTIONS_KIND_HUBPORT) {
-            error_set(errp, QERR_INVALID_PARAMETER_VALUE, "type",
-                      "a net type");
+            error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "type",
+                       "a net type");
             return -1;
         }
         /* missing optional values have been initialized to "all bits zero" */
@@ -975,8 +975,8 @@
         if (net_client_init_fun[opts->kind](opts, name, peer, errp) < 0) {
             /* FIXME drop when all init functions store an Error */
             if (errp && !*errp) {
-                error_set(errp, QERR_DEVICE_INIT_FAILED,
-                          NetClientOptionsKind_lookup[opts->kind]);
+                error_setg(errp, QERR_DEVICE_INIT_FAILED,
+                           NetClientOptionsKind_lookup[opts->kind]);
             }
             return -1;
         }