Support addr=... in option argument of -net nic

Make net_client_init() accept addr=, put the value into struct
NICinfo.  Use it in pci_nic_init(), and remove arguments bus and
devfn.

Don't support addr= in third argument of monitor command pci_add,
because that clashes with its first argument.  Admittedly unelegant.

Machines "malta" and "r2d" have a default NIC with a well-known PCI
address.  Deal with that the same way as the NIC model: make
pci_nic_init() take an optional default to be used when the user
doesn't specify one.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

net.h

@@ -88,6 +88,7 @@ struct NICInfo {
     uint8_t macaddr[6];
     const char *model;
     const char *name;
+    const char *devaddr;
     VLANState *vlan;
     void *private;
     int used;