libiproute: use itoa() where appropriate

libiproute: use itoa() where appropriate

function                                             old     new   delta
rtnl_rtprot_a2n                                       31      88     +57
print_tunnel                                         647     640      -7
print_route                                         1865    1858      -7
print_linkinfo                                       820     812      -8
print_addrinfo                                      1241    1227     -14
rtnl_rttable_n2a                                      53      38     -15
rtnl_rtscope_n2a                                      53      38     -15
rtnl_rtrealm_n2a                                      53      38     -15
rtnl_dsfield_n2a                                      61      38     -23
rtnl_rtntype_n2a                                     118      89     -29
print_rule                                           724     689     -35
ipaddr_list_or_flush                                1293    1253     -40
rtnl_rtprot_n2a                                       53       -     -53
rtnl_rtprot_initialize                                63       -     -63
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 1/11 up/down: 57/-324)         Total: -267 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>