Demand paging, the RTL8168H, links that come up late, and Ctrl+Alt+F1..F12

- Anonymous memory can be reserved without being backed: large mappings,
  MAP_NORESERVE and PROT_NONE are recorded and each page appears, zeroed,
  on first touch -- from trap() for the program, from uva2ka() for the
  kernel on its behalf. WebKit reserves 4 GB at start and touches a sliver;
  backing it all failed with ENOMEM and Epiphany aborted.
- r8169: the 8168G generation and later (the laptop's 8168H, XID 541) are
  taken from the firmware's out-of-band mode, get their PLL powered, the
  receive gate opened, and their PHY reached through the OCP window. The
  PHY's power-down bit is cleared; the old code kept it while restarting
  autonegotiation. Untested on the hardware so far.
- The network thread follows each device's link into lwIP. The link was
  read once at attach, 0.02 s into boot; real autonegotiation takes
  seconds, so on hardware the interface stayed down for good.
- Twelve terminals, switched with Ctrl+Alt+F1..F12 by default: the keys X
  uses, so the console and the desktop agree. AltGr+F-key is gone from
  the defaults (chvt -c altgr+F brings it back).
- SO_PASSCRED on Unix sockets, with SCM_CREDENTIALS delivered by recvmsg.
  WebKit sets it on its IPC sockets and aborted when refused.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

include/dev/kbd.h

@@ -92,12 +92,10 @@
 // leaves `chvt N` as the only way to switch, which is a legitimate choice on
 // a machine whose host takes everything.
 //
-// The default is AltGr+F1..F6, and the "AltGr wants it" line above needs
-// reading carefully: what a Polish layout wants is AltGr+*letter*. AltGr with
-// a function key produces nothing on any layout, no window manager binds it,
-// and no application asks for it. Right Alt being a separate modifier bit
-// here is what makes the distinction expressible at all -- it used to share
-// ALT, which is harmless for typing and useless for this.
+// The default is Ctrl+Alt+F1..F12: the keys X switches with, so the console
+// and the desktop answer the same chord. It used to be AltGr+F-key, which
+// nothing else claims -- Right Alt being a separate modifier bit here is what
+// makes that expressible, and `chvt -c altgr+F` still sets it.
 #define KBD_VT_SWITCH   (KBD_SPECIAL + 0x20)
 
 // Previous / next terminal, on the same modifiers as the chord above. The