net: consolidate NetClientState header files into one

This patch doesn't seem much useful alone, I must admit.  However,
it makes sense as part of the upcoming directory reorganization,
where I want to have include/net/tap.h as the net<->hw interface
for tap.  Then having both net/tap.h and include/net/tap.h does
not work.  "Fixed" by moving all the init functions to a single
header file net/clients.h.

The patch also adopts a uniform style for including net/*.h files
from net/*.c, without the net/ path.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
diff --git a/net/tap.c b/net/tap.c
index a88ae8f..df89caa 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -23,7 +23,7 @@
  * THE SOFTWARE.
  */
 
-#include "net/tap.h"
+#include "tap.h"
 
 #include "config-host.h"
 
@@ -34,6 +34,7 @@
 #include <net/if.h>
 
 #include "net.h"
+#include "clients.h"
 #include "monitor.h"
 #include "sysemu.h"
 #include "qemu-char.h"