IB/mthca: Fix dispatch of IB_EVENT_LID_CHANGE event

When snooping a PortInfo MAD, its client_reregister bit is checked.
If the bit is ON then a CLIENT_REREGISTER event is dispatched,
otherwise a LID_CHANGE event is dispatched.  This way of decision
ignores the cases where the MAD changes the LID along with an
instruction to reregister (so a necessary LID_CHANGE event won't be
dispatched) or the MAD is neither of these (and an unnecessary
LID_CHANGE event will be dispatched).

This causes problems at least with IPoIB, which will do a "light"
flush on reregister, rather than the "heavy" flush required due to a
LID change.

Fix this by dispatching a CLIENT_REREGISTER event if the
client_reregister bit is set, but also compare the LID in the MAD to
the current LID.  If and only if they are not identical then a
LID_CHANGE event is dispatched.

Signed-off-by: Moni Shoua <monis@voltaire.com>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Yossi Etigin <yosefe@voltaire.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>