Make the e1000 the default network adapter for the pc target.

The ne2k is an ancient card that performs pretty terribly under QEMU.  In many
modern OSes, there is no longer drivers available for the ne2k.

Switch the default network adapter to e1000.  This card is more widely
suppported and performs rather well under QEMU.  There may be very old OSes
that had a ne2k driver but not an e1000 driver but I think this is likely the
exception.

I think the average user is better served with an e1000 vs ne2k.
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/pc.c

@@ -1264,7 +1264,7 @@ static void pc_init1(ram_addr_t ram_size,
             continue;
 
         if (model == NULL)
-            model = "ne2k_pci";
+            model = "e1000";
         snprintf(nic_oprom, sizeof(nic_oprom), "pxe-%s.bin", model);
 
         oprom_area_size += load_option_rom(nic_oprom, 0xc0000 + oprom_area_size,
@@ -1347,7 +1347,7 @@ static void pc_init1(ram_addr_t ram_size,
         if (!pci_enabled || (nd->model && strcmp(nd->model, "ne2k_isa") == 0))
             pc_init_ne2k_isa(nd, isa_irq);
         else
-            pci_nic_init(nd, "ne2k_pci", NULL);
+            pci_nic_init(nd, "e1000", NULL);
     }
 
     piix4_acpi_system_hot_add_init();

qemu-options.hx

@@ -828,7 +828,7 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
 STEXI
 @item -net nic[,vlan=@var{n}][,macaddr=@var{mac}][,model=@var{type}][,name=@var{name}][,addr=@var{addr}][,vectors=@var{v}]
 Create a new Network Interface Card and connect it to VLAN @var{n} (@var{n}
-= 0 is the default). The NIC is an ne2k_pci by default on the PC
+= 0 is the default). The NIC is an e1000 by default on the PC
 target. Optionally, the MAC address can be changed to @var{mac}, the
 device address set to @var{addr} (PCI cards only),
 and a @var{name} can be assigned for use in monitor commands.