cast return class

to fit with the class wrapped by
h2py: update enum right hand regexp

might be expression
callback: fix control callbacks handling

did not work.
batch: fix class's constructor and current

it did not work
nlstructs: lack of ctypes imports
callback: use dict in cb_ctls

in case of list:
  ctlcbs = [None] * netlink.NLMSG_MIN_TYPE
  ctlcbs[netlink.NLMSG_ERROR] = cb_err

or dict:
  ctlcbs = {netlink.NLMSG_ERROR: cb_err}