IB/core: Remove ib_uverbs_flow_spec structure from userspace

The structure holding any types of flow_spec is of no use to
userspace.  It would be wrong for userspace to do:

  struct ib_uverbs_flow_spec flow_spec;

  flow_spec.type = IB_FLOW_SPEC_TCP;
  flow_spec.size = sizeof(flow_spec);

Instead, userspace should use the dedicated flow_spec structure for
  - Ethernet : struct ib_uverbs_flow_spec_eth,
  - IPv4     : struct ib_uverbs_flow_spec_ipv4,
  - TCP/UDP  : struct ib_uverbs_flow_spec_tcp_udp.

In other words, struct ib_uverbs_flow_spec is a "virtual" data
structure that can only be use by the kernel as an alias to the other.

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Link: http://marc.info/?i=cover.1383773832.git.ydroneaud@opteya.com
Signed-off-by: Roland Dreier <roland@purestorage.com>