IB/mlx4: Do IBoE locking earlier when initializing the GID table

Updating the GID table under IBoE requires read/write from/to shared
data structures.  These data structures are protected with the device
iboe lock.  The flows that modify the GID table start from

    1. Initializing the GID table
    2. NETDEV events
    3. INET or INET6 events

This patch makes sure that the flow of initializing the GID table is
consistent with the other two flows w.r.t on what step the lock is taken.

Signed-off-by: Moni Shoua <monis@mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>