ofproto: Rename *_begin functions as *_start.

ofproto: Rename *_begin functions as *_start.

Weirdest things can bother you at night when you try to sleep ;-)

Now we have function triples such as add_flow_begin(),
add_flow_finish(), and add_flow_revert(), where a modification is
started in *_begin(), which can fail, and when successful can be
either made permanent with *_finish(), or cancelled with *_revert().

Linguistically it should be either "begin/end" or "start/finish", not
"begin/finish".  "begin/end" has some C++ STL baggage, so let's go
with "start/finish".  IMO "revert" rhymes with it, too.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>