IB/uverbs: Add support to extend flow steering specifications

Flow steering specifications structures were implemented as in an
extensible way that allows one to add new filters and new fields
to existing filters.
These specifications have never been extended, therefore the
kernel flow specifications size and the user flow specifications size
were must to be equal.

In downstream patch, the IPv4 flow specifications type is extended to
support TOS and TTL fields.

To support an extension we change the flow specifications size
condition test to be as following:

* If the user flow specifications is bigger than the kernel
specifications, we verify that all the bits which not in the kernel
specifications are zeros and the flow is added only with the kernel
specifications fields.

* Otherwise, we add flow rule only with the user specifications fields.

User space filters must be aligned with 32bits.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>