Avoids races of high-level syscons code with the sckbdevent handler.

Made for FreeBSD 7.x (syscons.c 1.453.2.1); was tested on
7.0-PRERELEASE, 7.0-STABLE, 7.0-RELEASE-p3 and 7.1-PRERELEASE (up to
the revision 1.453.2.3 of syscons.c).

--- sys/dev/syscons/syscons.c.orig	2008-09-23 11:46:45.000000000 +0400
+++ sys/dev/syscons/syscons.c	2008-09-23 12:16:32.000000000 +0400
@@ -1590,6 +1592,7 @@
     int s = spltty();	/* block sckbdevent and scrn_timer while we poll */
     int c;
 
+    mtx_lock(&Giant);
     /* assert(sc_console != NULL) */
 
     /* 
@@ -1601,11 +1604,13 @@
     sccnupdate(scp);
 
     if (fkeycp < fkey.len) {
+	mtx_unlock(&Giant);
 	splx(s);
 	return fkey.str[fkeycp++];
     }
 
     if (scp->sc->kbd == NULL) {
+	mtx_unlock(&Giant);
 	splx(s);
 	return -1;
     }
@@ -1628,6 +1633,7 @@
     scp->kbd_mode = cur_mode;
     kbd_ioctl(scp->sc->kbd, KDSKBMODE, (caddr_t)&scp->kbd_mode);
     kbd_disable(scp->sc->kbd);
+    mtx_unlock(&Giant);
     splx(s);
 
     switch (KEYFLAGS(c)) {