Update epair(4) to the new netisr implementation and polish

things a bit:
- use dpcpu data to track the ifps with packets queued up,
- per-cpu locking and driver flags
- along with .nh_drainedcpu and NETISR_POLICY_CPU.
- Put the mbufs in flight reference count, preventing interfaces
  from going away, under INVARIANTS as this is a general problem
  of the stack and should be solved in if.c/netisr but still good
  to verify the internal queuing logic.
- Permit changing the MTU to virtually everythinkg like we do for loopback.

Hook epair(4) up to the build.

Approved by:	re (kib)

2 files changed, 5 insertions, 0 deletions

diff --git a/sys/conf/NOTES b/sys/conf/NOTES
index 37ffa1c..b448f94 100644
--- a/sys/conf/NOTES
+++ b/sys/conf/NOTES
@@ -784,6 +784,10 @@ device		bpf
 #  included for testing and benchmarking purposes.
 device		disc
 
+# The `epair' device implements a virtual back-to-back connected Ethernet
+# like interface pair.
+device		epair
+
 #  The `edsc' device implements a minimal Ethernet interface,
 #  which discards all packets sent and receives none.
 device		edsc
diff --git a/sys/conf/files b/sys/conf/files
index 298b409..8c654c7 100644
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -2202,6 +2202,7 @@ net/if_disc.c			optional disc
 net/if_edsc.c			optional edsc
 net/if_ef.c			optional ef
 net/if_enc.c			optional enc ipsec inet | enc ipsec inet6
+net/if_epair.c			optional epair
 net/if_ethersubr.c		optional ether \
 	compile-with "${NORMAL_C} -I$S/contrib/pf"
 net/if_faith.c			optional faith