NI_MAXSERV: remove all use of it

Solaris with the SunStudio Compiler is reportedly missing this define,
but as we're using it without any good reason on all the places it was
used I've now instead switched to just use sensible buffer sizes that
fit a 32 bit decimal number. Which also happens to be smaller than the
common NI_MAXSERV value which is 32 on most machines.

Bug: http://curl.haxx.se/bug/view.cgi?id=1277
Reported-by: D.Flinkmann