other "system" header files.
Also help the deprecation of lockmgr.h by making it a sub-include of
sys/lock.h and removing sys/lockmgr.h form kernel .c files.
Sort sys/*.h includes where possible in affected files.
OK'ed by: bde (with reservations)
Use mchain API to work with mbuf chains.
Do not depend on INET and IPX options.
Allocate ncp_rq structure dynamically to prevent possible stack overflows.
Let ncp_request() dispose control structure if request failed.
Move all NCP wrappers to ncp_ncp.c file and all NCP request processing
functions to ncp_rq.c file.
Improve reconnection logic.
Misc style fixes.
Add lockdestroy() and appropriate invocations, which corresponds to
lockinit() and must be called to clean up after a lockmgr lock is no
longer needed.
