fabric: Move open_if operation to struct fi_ops

Allow any structure to support extended operations.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Merge pull request #64 from shefty/master

fabric: Move open_if operation to struct fi_ops
include: optional function availability by macros

Some functions - inject, eq_readfrom, etc. are optional for
providers. This patch introduces macros that enable applications
to check if these functions are available.

Signed-off-by: Sayantan Sur <sayantan.sur@intel.com>
Merge pull request #65 from sayantansur/fi-optional-functions

include: optional function availability by macros