1) move all link state detection code from bge_tick_locked() to bge_link_upd()

1) move all link state detection code from bge_tick_locked() to bge_link_upd()
2) use more robust way of link state handling for BCM5700 rev.B2 chip
3) workaround bug of some BCM570x chips which cause spurious "link up" messages
4) fix bug: some BCM570x chips was unable to detect link state changes after
   ifconfig down/up sequence until any 'non-link related' interrupt generated.
   (this happened due to pending internal link state attention which blocked
   interrupt generation)

Approved by:	glebius (mentor)
MFC after:	1 week