The following diff fixes the gem(4) driver to properly set and clear
the IFF_OACTIVE flag as appropriate to indicate to the upper layer
that the adapter has run out of TX descriptors.

Please test with any gem(4) adapters.

Index: gem.c
===================================================================
RCS file: /cvs/src/sys/dev/ic/gem.c,v
retrieving revision 1.73
diff -u -p -r1.73 gem.c
--- gem.c 10 Feb 2008 16:54:23 -0000 1.73
+++ gem.c 1 Apr 2008 21:32:46 -0000
@@ -807,7 +807,6 @@ gem_init(struct ifnet *ifp)

ifp->if_flags |= IFF_RUNNING;
ifp->if_flags &= ~IFF_OACTIVE;
- ifp->if_timer = 0;
splx(s);