kernel/netgraph7: Port the kernel part of the netgraph7 bluetooth stack.

It still needs more testing/debugging, along with the userland part.

In-discussion-with: nant

Netgraph port from FreeBSD - initial porting work

* Use relative #include's as appropriate so the code doesn't
dig into the original netgraph/ directory.

* Move FBSDID's and add DragonFly ids.

*

Netgraph port from FreeBSD - initial porting work

* Use relative #include's as appropriate so the code doesn't
dig into the original netgraph/ directory.

* Move FBSDID's and add DragonFly ids.

* Fix improper uses of M_NOWAIT.

* Fix uses of M_NOWAIT which should be MB_DONTWAIT and vise-versa
(also forward to Julian).

* Add a dragonfly.h compatibility header.

* NOTE: m_tag_alloc() in DFly takes MB_ flags.

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Vendor import of netgraph from FreeBSD-current 20080626