iproute/iprule: support toolchains without RTA_TABLE routing attribute

iproute/iprule: support toolchains without RTA_TABLE routing attribute

 iproute.c: In function 'print_route':
 iproute.c:85:9: error: 'RTA_TABLE' undeclared (first use in this function)
 iproute.c:85:9: note: each undeclared identifier is reported only once for each function it appears in
 iproute.c: In function 'iproute_modify':
 iproute.c:467:36: error: 'RTA_TABLE' undeclared (first use in this function)

Fix it by partially #ifdef'ing the code added in b42107f21538e39d9a344376372f8261aed589b2

Signed-off-by: Eugene Rudoy <gene.devel@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>