RDS: add module parameter to allow module unload or not

RDS: add module parameter to allow module unload or not

orabug: 19665303

This patch adds the following feature to ib_ipoib, rds_rdma, ib_core and
mlx4_core.

Adds a module parameter "module_unload_allowed". If the parameter is 1(the
default value), moudles can be unloaded(same behavior as before); other-
wise if it's 0, the module is not allowed to be unloaded. The paramter can't
be changed when module is loaded until the module is unloaded(if it can be).

default values:
ib_ipoib: 1 for YES
rds_rdma: 0 for NO
ib_core: 1 for YES
mlx4_core: 0 for NO

Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
Acked-by: Joe Jin <joe.jin@oracle.com>
Acked-by: Todd Vierling <todd.vierling@oracle.com>
Acked-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Guangyu Sun <guangyu.sun@oracle.com>
(cherry picked from commit cf1a00039e6fea116e9ea7c82f55ee3ee5319cec)

Conflicts:
	drivers/infiniband/core/device.c
	drivers/infiniband/ulp/ipoib/ipoib_main.c
	drivers/net/ethernet/mellanox/mlx4/main.c