Kernel: Instantiate network adapters in their own detect() methods

This commit is one step forward for pluggable driver modules.
Instead of creating instances of network adapter classes, we let
their detect() methods to figure out if there are existing devices
to initialize.

Kernel/PCI/Initializer.cpp

@@ -58,11 +58,8 @@ void initialize()
         MMIOAccess::initialize(ACPI::Parser::the()->find_table("MCFG"));
     else
         IOAccess::initialize();
-
-    enumerate([&](const Address& address, ID id) {
+    PCI::enumerate([&](const Address& address, ID id) {
         klog() << address << " " << id;
-        E1000NetworkAdapter::detect(address);
-        RTL8139NetworkAdapter::detect(address);
     });
 }