Restore the check for non-NULL dmatag in sndbuf_free.

The sound drivers that use own buffer management can use sndbuf_setup
and not do any busdma allocation, so the driver will end up with the
managed buffer but no valid dma map and tag for it. Avoid calling
bus_dmamem_free in such cases.

Reported by: ache
Missed in review by: kan
Catch up with r186809, correct comments.
Use correct names for the flags.  MAP_ENTRY_GROWS_* have the same
numerical values as MAP_STACK_GROWS_*, but the former is for entries'
eflags, while the later for the cow argument of vm_map_insert().

Submitted by:	alc
Add FPU_KERN_KTHR flag to fpu_kern_enter(9), which avoids saving FPU
context into memory for the kernel threads which called
fpu_kern_thread(9).  This allows the fpu_kern_enter() callers to not
check for is_fpu_kern_thread() to get the optimization.

Apply the flag to padlock(4) and aesni(4).  In aesni_cipher_process(),
do not leak FPU context state on error.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Add documentation for the fpu_kern(9) interfaces.

Many thanks to jmg for reviewing the (previous version) of the text
and providing grammar and content fixes.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
use .Mt to mark up email addresses consistently (part3)

PR:		191174
Submitted by:	Franco Fichtner  <franco at lastsummer.de>
use .Mt to mark up email addresses consistently (part4)

PR:		191174
Submitted by:	Franco Fichtner  <franco at lastsummer.de>
use .Mt to mark up email addresses consistently (part6)

PR:		191174
Submitted by:	Franco Fichtner <franco at lastsummer.de>
Several small fixes (typos, grammar, mdoc).
Fix markup and grammar.
Exclude IPv4 address from doing longest match.
It prevented DNS based load balancing.

MFC after:	1 week
Make nd6_gctimer tunable.

MFC after:	1 week
With the move away from GNATS, drop the CTM config file for downloading
the GNATS database, it will be going away soon.
mdoc: remove superfluous paragraph macros.
Provide APIs to directly get 'lowmem' and 'highmem' size directly.

Previously the sizes were inferred indirectly based on the size of the mappings
at 0 and 4GB respectively. This works fine as long as size of the allocation is
identical to the size of the mapping in the guest's address space. However, if
the mapping is disjoint then this assumption falls apart (e.g., due to the
legacy BIOS hole between 640KB and 1MB).