Grammar fix

Submitted by:	Warren Block wblock AT wonkity.com
Simplify the way the end of a singly linked list is followed (for adding
items), so it is more obvious that we aren't going to indirect through
a NULL pointer.

PR:		144723
Submitted by:	Garrett Cooper <yaneurabeya at gmail.com>
Obtained from:	NetBSD r1.19
MFC after:	2 weeks
Increase alignment to size of pointer if the alignment is too small.
Some modules do not align data at least to size of pointer, they uses a
smaller alignment, but our pointer should be aligned to its native
boundary, otherwise on some platforms, hardware alignment checking
will cause bus error.
Rename WITHOUT_DMA into WITHOUT_DMAGENT to avoid confusion

Requested by:	ian
Regen after WITHOUT_DMA -> WITHOUT_DMAGENT renaming