zebra: adapt zebra_pbr_rule based with pbr_rule

zebra: adapt zebra_pbr_rule based with pbr_rule

In order to avoid duplicates functions, the zebra_pbr_rule structure
used by zebra to decode the zapi message, and send netlink messages, is
slightly modified. the structure is derived from pbr_rule, but it also
includes sock identifier that is used to send back information to the
daemon that did the request. Also, the ifp pointer is stored in that
structure.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>