net/mlx4_core: Initialize IB port capabilities for all slaves

With IB SR-IOV, each slave has its own separate copy of the port
capabilities flags.  For example, the master can run a subnet manager
(which causes the IsSM bit to be set in the master's port
capabilities) without affecting the port capabilities seen by the
slaves (the IsSM bit will be seen as cleared in the slaves).

Also add a static inline mlx4_master_func_num() to enhance readability
of the code.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>