RDMA/rtrs: Do not allow sessname to contain special symbols / and .

RDMA/rtrs: Do not allow sessname to contain special symbols / and .

Allowing these characters in sessname can lead to unexpected results,
particularly because / is used as a separator between files in a path, and
. points to the current directory.

Link: https://lore.kernel.org/r/20210922125333.351454-7-haris.iqbal@ionos.com
Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Reviewed-by: Gioh Kim <gi-oh.kim@ionos.com>
Reviewed-by: Aleksei Marov <aleksei.marov@ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>