sync the code with the version in head. which the exception of
svn 275358 (M_FLOWID deprecation, only a couple of lines)
which cannot be merged.

if_lem_netmap.h, if_re_netmap.h:

• use the same (commented out) function to update the stat counters as in HEAD. This is a no-op here

netmap.c

• merge 274459 (support for private knote lock) and minor changes on nm_config and comments

netmap_freebsd.c

• merge 274459 (support for private knote lock)
• merge 274354 (initialize color if passed as argument)

netmap_generic.c

• fix a comment

netmap_kern.h

• revise the lock macros, using sx locks; merge 274459 (private knote lock)

netmap_monitor.c

• use full memory barriers

netmap_pipe.c

• use full memory barriers, use length from the correct queue (mostly cosmetic, since the queues typically have the same size)