Add option WITNESS_NO_VNODE to suppress printing LORs between VNODE
locks. To support this, VNODE locks are created with the LK_IS_VNODE
flag. This flag is propagated down using the LO_IS_VNODE flag.

Note that WITNESS still records the LOR. Only the printing and the
optional entering into the kernel debugger is bypassed with the
WITNESS_NO_VNODE option.
posix_spawn_file_actions_addopen(3): Correct error for bad file descriptor.

As per POSIX.1-2008, posix_spawn_file_actions_add* return [EBADF] if a file
descriptor is negative, not [EINVAL]. The bug was only in the manual page;
the code is correct.

MFC after:	1 week
simplify the code to initialize the RDT while in netmap mode.
if_lem.c:  make sure that lem_rxeof() can drain the entire rx queue
	irrespective of the setting of lem_rx_process_limit, while
	giving a chance to the taskqueue scheduler to act after
	each chunk.
	This makes lem_rxeof similar to the one in if_em.c and if_igb.c .

if_lem.c and if_em.c: add a sysctl to manually configure the
	'itr' moderation register.

Approved by:	Jack Vogel