Each of the ypclnt functions does a _yp_dobind() when it starts and then
a _yp_unbind() when it finishes. This is not strictly necessary and it
wastes cycles: it means we do a new clnt_create() and clnt_destroy()
for each yp_whatever() call. In fact, you can do multiple clnt_call()s
using a single RPC client handle returned by clnt_create(). Ideally we only
have to create a handle to ypserv once (the first time we call a ypclnt
function) and then destroy it and rebind only if a call to ypserv fails.
- Modify _yp_dobind() so that it only creates a new RPC client handle
when establishing a new binding or when one of the ypclnt calls
invalidates an existing binding and calls _yp_dobind() to establish
a new one.
- Modify the various ypclnt functions to only call _yp_unbind() if a
call to ypserv fails.