SUNRPC: Rename "call_" functions that are no longer FSM states

The RPC client uses a finite state machine to move RPC tasks through each
step of an RPC request.  Each state is contained in a function in
net/sunrpc/clnt.c, and named call_foo.

Some of the functions named call_foo have changed over the past few years and
are no longer states in the FSM.  These include: call_encode, call_header,
and call_verify.  As a clean up, rename the functions that have changed.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>