crash the machine.

tracking down a bug that turned out to be a free_iob() used where I
needed a netdev_tx_complete().  This left the freed I/O buffer on the
net device's TX list, with bad, bad consequences later.

Also fixed the bug in question.

the assert message's file and line number gives some clue as to the
real location of the problem.

Added similar assertions to list.h.

makes it easier to put the generic allocation code into infiniband.c

the number of separate allocations that need to be done).

using entirely our own code.