kernel: timers that fire, raw ping, and the sockets X needs

alarm() and setitimer() stored a countdown nothing counted down, so no
timer has ever fired; setitimer and getitimer were also registered with
no Linux number. alarmd now posts SIGALRM on the tick, while any process
has a timer armed. busybox's ping, /bin/ping on the Alpine root, sends
every request after the first from its SIGALRM handler.

It also opens SOCK_RAW, which was EPROTOTYPE. A raw ICMP socket is now a
ping socket whose reads start at the IP header. And a blocked socket
call gives up for a signal with a handler, not only for a kill: the
alarm woke recvfrom, and the wait put it straight back to sleep.

For Xorg: AF_UNIX abstract names, which read as the empty path and so as
EADDRINUSE ("server already running"); and getsockname and getpeername,
which did not exist, so libxcb sent no cookie and the server refused
every client.

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

include/core/proc.h

@@ -231,7 +231,11 @@ struct proc {
 
   uint64 signal_mask;
   uint64 pending_signals;
-  int alarm_ticks;
+  // ITIMER_REAL, which alarm() is the whole-second form of: SIGALRM is due at
+  // tick alarm_at (0 = not armed) and then every alarm_every ticks after.
+  // alarmd, in kernel/proc/proc.c, is what posts it.
+  uint alarm_at;
+  uint alarm_every;
   char ofile_flags[NOFILE];
 
   // Real signal delivery (added for SIGCHLD — see kernel/sys/syscall.c's