pimd: add a workaround for *BSD

pimd: add a workaround for *BSD

VIFF_USE_IFINDEX is not available on BSDs and other UNIX systems. In
order to build pimd on these platforms, use 'vifc_lcl_addr' instead of
'vifc_lcl_ifindex' to specify the interfaces we want to enable forwarding
of multicast traffic. In the case of unnumbered interfaces, print an
error and return.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>