Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Mechanically substitute flags from historic mbuf allocator with
malloc(9) flags within sys.

Exceptions:

- sys/contrib not touched
- sys/mbuf.h edited manually

Remove a few bits of FreeBSD 2.x compatibility code.

Approved by: kib (mentor)

Tag mbufs of all incoming frames or packets with the interface's FIB
setting (either default or if supported as set by SIOCSIFFIB, e.g.
from ifconfig).

Submitted by: Alexander V. Chernikov (melifaro ipfw.ru)
Reviewed by: julian
MFC after: 2 weeks

Stop embedding struct ifnet at the top of driver softcs. Instead the
struct ifnet or the layer 2 common structure it was embedded in have
been replaced with a struct ifnet pointer to be filled by a call to the
new function, if_alloc(). The layer 2 common structure is also allocated
via if_alloc() based on the interface type. It is hung off the new
struct ifnet member, if_l2com.

This change removes the size of these structures from the kernel ABI and
will allow us to better manage them as interfaces come and go.

Other changes of note:
- Struct arpcom is no longer referenced in normal interface code.
Instead the Ethernet address is accessed via the IFP2ENADDR() macro.
To enforce this ac_enaddr has been renamed to _ac_enaddr.
- The second argument to ether_ifattach is now always the mac address
from driver private storage rather than sometimes being ac_enaddr.

Reviewed by: sobomax, sam

/* -> /*- for license, minor formatting changes

Add FR support to sppp (MFCronyx).

Silence on: net@, current@, hackers@.
No objections: joerg

Requested by: by many (mostly Cronyx) users for a long long time.
MFC after: 10 days

PR: kern/21771, kern/66348