[ATM] a few more changes for people to test

[chas williams]

besides the previous changes, this release:

. should no longer race when opening vcc's -- atm_find_ci is obselete
  the upper layer always allocates the vpi/vci with the proper locking
  held
. fixes a race for device numbering in atm_dev_register()
. make the list of vcc's global.  this simplifies the code quite a bit,
  and for a vast majority (single atm card) its essentially the same.
. converts vcc->itf to vcc->sk->bound_dev_if
. lets proc/fore200e/eni walk the vcc list safely now

i think locking in the bottom halves of the nicstar/idt77252 is now correct.
since i dont have any idt77252 cards, i only tested the nicstar but the 
code is essentially the same.  the lanai and iphase drivers need similar
work done.  anyone willing to test some changes?  (again, i dont have these
cards).

ftp://ftp.cmf.nrl.navy.mil/pub/chas/linux-atm/2_5_66_diffs
ftp://ftp.cmf.nrl.navy.mil/pub/chas/linux-atm/2_4_20_diffs