*: move get_sock_lsa and xwrite_str to libbb, use where appropriate

*: move get_sock_lsa and xwrite_str to libbb, use where appropriate

function                                             old     new   delta
get_sock_lsa                                           -      72     +72
buffer_fill_and_print                                179     196     +17
parse_expr                                           824     832      +8
read_base64                                          343     348      +5
nameval                                              202     206      +4
fbset_main                                          1694    1698      +4
expand                                              1849    1853      +4
udhcp_send_kernel_packet                             249     252      +3
udhcp_get_option                                     223     222      -1
chat_main                                           1246    1245      -1
pack_gzip                                           1661    1659      -2
doset                                                299     297      -2
bb__parsespent                                       119     117      -2
test_main                                            260     257      -3
qgravechar                                           109     106      -3
tcpudpsvd_main                                      1834    1830      -4
sysctl_display_all                                   589     580      -9
xopen_xwrite_close                                    44      33     -11
prs                                                   30      18     -12
find_main                                            418     406     -12
full_write2_str                                       25      12     -13
adduser_main                                         667     654     -13
evaltreenr                                           817     802     -15
evaltree                                             817     802     -15
tftpd_main                                           526     493     -33
ftpd_main                                           2050    1990     -60
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 7/18 up/down: 117/-211)         Total: -94 bytes