rtnl_rule: decode new FRA_* attributes

rtnl_rule: decode new FRA_* attributes

* nlattr.h (DECL_NLA(ip_proto), DECL_NLA(rt_proto)): New declarations.
* nlattr.c (decode_nla_ip_proto): New function.
* rtnl_route.c (decode_nla_rt_proto): Likewise.
* rtnl_rule.c (decode_rule_port_rang): Likewise.
(fib_rule_hdr_nla_decoders) <[FRA_PROTOCOL]>: New attribute, introduced
by Linux commit v4.17-rc1~148^2~371.
(fib_rule_hdr_nla_decoders) <[FRA_IP_PROTO], [FRA_SPORT_RANGE],
[FRA_DPORT_RANGE]>: New attributes, introduced by Linux commit
v4.17-rc1~148^2~328^2~4.
* xlat/rtnl_rule_attrs.in (FRA_PROTOCOL, FRA_IP_PROTO, FRA_SPORT_RANGE,
FRA_DPORT_RANGE): New constants.

Co-Authored-by: Dmitry V. Levin <ldv@altlinux.org>