netmsg: Update comment
arp: Embed netmsg_inarp in mbuf for asynchronized ARP input processing

- Embed netmsg_inarp, which records necessary states for routing table
  updating and later ARP reply, into mbuf; this does not change mbuf
  header size.
- If routing tables need updating upon ARP packet reception, the
  netmsg_inarp embedded in the input ARP packet is sent asynchronizingly
  to routing threads and the possible ARP reply is defered until all
  routing tables are updated, i.e. the ARP packet is redispatched to
  netisr0 for the ARP reply sending from the last routing thread.
- Remove no longer needed dedicated network threads.

Discussed-with: dillon@
kernel/i386: Use offsetof() here.
kernel - Remove symbol space corruption from ncp_conn.h

* ncp_conn.h was #defining 'ipxaddr', 'inaddr', and 'saddr', all
  commonly used variable names.  This was interfering with netmsg.h.

* Remove the definitions, replace use cases with expansion.
kernel - Remove symbol space corruption from ncp_conn.h (2)

* libncp also needed adjustment.
kernel - Beef up lwkt_dropmsg() API and fix deadlock in so_async_rcvd*()

* Beef up the lwkt_dropmsg() API.  The API now conditionally returns
  success (0) or an error (ENOENT).

* so_pru_rcvd_async() improperly calls lwkt_sendmsg() with a spinlock
  held.  This is not legal.  Hack up lwkt_sendmsg() a bit to resolve.
kernel - Fix panic on ptrace termination

* Fix a panic in the situation where gdb is exiting and terminating
  a ptrace, but the original parent prpocess of the process being
  debugged no longer exists.
kernel - Fix vm.shared_fault for vkernels and 32-bit

* The pmap code needed the same changes as were made to the 64-bit
  pmap code to avoid a live lock.

Reported-by: davshao, tuxillo
kernel - Fix shared/excl livelock with vm.shared_fault

* The vop_helper_read_shortcut() code was holding a shared token on
  a VM object through a uiomove().  If the uiomove() generated a VM
  fault requiring a shadow copy, the shadow copy would try to get
  an exclusive token on potentially the same object and livelock.

* Fix by unlocking/relocking across the uiomove().
Merge branch 'master' into gsocdrm_jfree