Include qapi/error.h exactly where needed

This cleanup makes the number of objects depending on qapi/error.h
drop from 1910 (out of 4743) to 1612 in my "build everything" tree.

While there, separate #include from file comment with a blank line,
and drop a useless comment on why qemu/osdep.h is included first.

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180201111846.21846-5-armbru@redhat.com>
[Semantic conflict with commit 34e304e975 resolved, OSX breakage fixed]

hw/net/rocker/qmp-norocker.c

@@ -18,6 +18,7 @@
 #include "qemu/osdep.h"
 #include "qemu-common.h"
 #include "qmp-commands.h"
+#include "qapi/error.h"
 #include "qapi/qmp/qerror.h"
 
 RockerSwitch *qmp_query_rocker(const char *name, Error **errp)

hw/net/rocker/rocker.c

@@ -21,6 +21,7 @@
 #include "hw/pci/msix.h"
 #include "net/net.h"
 #include "net/eth.h"
+#include "qapi/error.h"
 #include "qemu/iov.h"
 #include "qemu/bitops.h"
 #include "qmp-commands.h"

hw/net/rocker/rocker_of_dpa.c

@@ -16,6 +16,7 @@
 
 #include "qemu/osdep.h"
 #include "net/eth.h"
+#include "qapi/error.h"
 #include "qemu/iov.h"
 #include "qemu/timer.h"
 #include "qmp-commands.h"

hw/net/virtio-net.c

@@ -22,6 +22,7 @@
 #include "hw/virtio/virtio-net.h"
 #include "net/vhost_net.h"
 #include "hw/virtio/virtio-bus.h"
+#include "qapi/error.h"
 #include "qapi/qmp/qjson.h"
 #include "qapi-event.h"
 #include "hw/virtio/virtio-access.h"