ngircd.c, main(): use strlcat() instead of strcat()

ngircd.c, main(): use strlcat() instead of strcat()

This fixes the following warning on OpenBSD 5.3:

 ngircd.o(.text+0xeb4): In function `main':
  src/ngircd/ngircd.c:300: warning: strcat() is almost always misused,
                                    please use strlcat()

Thanks to Götz Hoffart for reporting this!