When a netmap process terminates without the full set of buffers it
was granted via rings and ni_bufs_list_head represented in those rings
and lists (e.g., via SIGKILL), those buffers are no longer available
for subsequent users for the lifetime of the system. To mitigate this
resource leak, reset the allocator state when the last ref to that
allocator is released.

Note that this only recovers leaked resources for an allocator when
there are no longer any users of that allocator, so there remain
circumstances in which leaked allocator resources may not ever be
recovered - consider a set of multiple netmap processes that are all
using the same allocator (say, the global allocator) where members of
that set may be killed and restarted over time but at any given point
there is one member of that set running.

(vtnet and cxgbe not merged yet because we need some other mfc first)

- fix handling of tx mbufs in emulated netmap mode;
- introduce mbq_lock() and mbq_unlock()
- rate limit some error messages
- many whitespace and comment fixes

(enhanced VALE switch, netmap pipes, emulated netmap mode).
See details in the log for svn 261909.

remove $Id$ lines, and add blank lines around some #if / #elif /#endif

- remove vestiges of the old memory allocator
- clean up some comments

Submitted by: Hugh Nhan