Add generic list, status, load and unload docs to gpart(8)

- In the style of gmirror(8).

PR:		docs/191534
Reviewed by:	gavin
For reasons which are not clear, r254263 broke some PCMCIA and CardBus
bridges in strange ways, either rendering them unable to detect
insertion and removal events, or possibly unable to read from the
device behind the bridge.

This fixes at least one laptop, a Toshiba Tecra M5 with a Texas
Instruments PCxx12 (d=0x8039 v=0c104c) bridge.  The very similar
Tecra M9 has the same bridge, but worked fine without this change.

The bridge chip has no I/O port BAR, and there is nothing in the spec
to suggest I/O decoding should be enabled; however enabling it fixes
the issue.  Add an XXX comment to this effect.

Discussed with:	jhb, imp
MFC after:	2 weeks
Partial revert of r262867.

r262867 was described as fixing socket buffer checks for SOCK_SEQPACKET,
but also changed one of the SOCK_DGRAM code paths to use the new
sbappendaddr_nospacecheck_locked() function.  This lead to SOCK_DGRAM
bypassing socket buffer limits.
Improve locking of multicast addresses in VLAN and LAGG interfaces.

This fixes several scenarios of reproducible panics, cause by races
between multicast address changes and interface destruction.

MFC after:	2 weeks
Add support for Windows dialect of EXTENDED COPY command, aka Microsoft ODX.

This allows to avoid extra network traffic when copying files on NTFS iSCSI
disks within one storage host by drag'n'dropping them in Windows Explorer
of Windows 8/2012.  It should also accelerate Hyper-V VM operations, etc.

MFC after:	2 weeks
Sponsored by:	iXsystems, Inc.