svn revisions r269964 and r269963 seemed to have impaired small memory
footprint systems(32M/64M) and didn't leave enough free memory to load modules
when it was setting up page tables that for sizes that are never used on
these smallish boards.

Set kmem_zmax to PAGE_SIZE on these smaller systems (< 128M) to keep this
from happening. Verified on mips32 h/w.

PR:             193465
Submitted by:   delphij
Reviewed by:    adrian
Simplify legacy reservation handling.  Drop it on I_T nexus loss.
Improve transmit sending offload, TSO, algorithm in general.

The current TSO limitation feature only takes the total number of
bytes in an mbuf chain into account and does not limit by the number
of mbufs in a chain. Some kinds of hardware is limited by two
factors. One is the fragment length and the second is the fragment
count. Both of these limits need to be taken into account when doing
TSO. Else some kinds of hardware might have to drop completely valid
mbuf chains because they cannot loaded into the given hardware's DMA
engine. The new way of doing TSO limitation has been made backwards
compatible as input from other FreeBSD developers and will use
defaults for values not set.

Reviewed by:	adrian, rmacklem
Sponsored by:	Mellanox Technologies
MFC after:	1 week
Fix UNMAP stuck if the last block descriptor in the list is empty.

MFC after:	3 days
Register /usr/tests/lib/libproc to fix build.

Missed in r271937, reviewed in D710.