prov/sock: Correct calls to ep_rx_ctx and ep_tx_ctx functions

The prototype for these calls changed the to use a different instantiation
of the fid_ep structure, i.e. fid_sep

Signed-off-by: Jay Sternberg <jay.e.sternberg@intel.com>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Merge pull request #359 from shefty/master

prov/sock: Correct calls to ep_rx_ctx and ep_tx_ctx functions