introduce and use xdup2(int, int)

introduce and use xdup2(int, int)
stop checking whether setsockopt_reuseaddr(int fd) was successful (it always is)
remove second parameter (sockllen) from xmalloc_sockaddr2xxxxx functions

sockaddr2str                                         142     156     +14
collect_blk                                          467     474      +7
xdup2                                                 28      33      +5
singlemount                                         4456    4454      -2
print_host                                           214     212      -2
nslookup_main                                        139     137      -2
ftpgetput_main                                       414     412      -2
udhcpd_main                                         1258    1255      -3
udhcpc_main                                         2405    2402      -3
traceroute_main                                     4125    4122      -3
nc_main                                             1072    1069      -3
buffer_fill_and_print                                 76      73      -3
xmalloc_sockaddr2hostonly_noport                      18      14      -4
xmalloc_sockaddr2host_noport                          18      14      -4
xmalloc_sockaddr2host                                 15      11      -4
xmalloc_sockaddr2dotted_noport                        18      14      -4
xmalloc_sockaddr2dotted                               18      14      -4
wget_main                                           2618    2614      -4
ping_main                                            393     389      -4
ip_port_str                                          120     115      -5
dhcprelay_main                                      1146    1141      -5
dnsd_main                                           1531    1525      -6
passwd_main                                         1110    1102      -8
udhcp_kernel_packet                                  206     197      -9
udhcp_listen_socket                                  154     144     -10
getty_main                                          2576    2566     -10
setup                                                655     640     -15
xmove_fd                                              51      34     -17
dolisten                                             759     742     -17
tcpudpsvd_main                                      1866    1836     -30
startservice                                         339     299     -40