command-line: add ovs_cmdl_ prefix

command-line: add ovs_cmdl_ prefix

The coding style guidelines include the following:

  - Pick a unique name prefix (ending with an underscore) for each
    module, and apply that prefix to all of that module's externally
    visible names.  Names of macro parameters, struct and union members,
    and parameters in function prototypes are not considered externally
    visible for this purpose.

This patch adds the new prefix to the externally visible names.  This
makes it a bit more obvious what code is coming from common command
line handling code.

Signed-off-by: Russell Bryant <rbryant@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>