ofproto-dpif: Rename "recurse" to "indentation".

ofproto-dpif: Rename "recurse" to "indentation".

The "recurse" member of struct xlate_in and struct xlate_ctx is used for
two purposes: to determine the amount of indentation in "ofproto/trace"
output and to limit the depth of recursion.  An upcoming commit will
separate these tasks, and so in preparation this commit renames "recurse"
to "indentation".

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Ryan Moats <rmoats@us.ibm.com>