conf/ile: make sure buffer is large enough

conf/ile: make sure buffer is large enough

conf.c: In function 'lxc_assign_network':
conf.c:3096:25: error: '%lu' directive output may be truncated writing between 1 and 20 bytes into a region of size 19 [-Werror=format-truncation=]
   snprintf(pidstr, 19, "%lu", (unsigned long) pid);
                         ^~~
conf.c:3096:24: note: using the range [1, 18446744073709551615] for directive argument
   snprintf(pidstr, 19, "%lu", (unsigned long) pid);
                        ^~~~~
In file included from /usr/include/stdio.h:938:0,
                 from conf.c:35:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:64:10: note: format output between 2 and 21 bytes into a destination of size 19
   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        __bos (__s), __fmt, __va_arg_pack ());
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
confile.c: In function 'network_new_hwaddrs':
confile.c:2889:38: error: '%02x' directive output may be truncated writing between 2 and 8 bytes into a region of size 6 [-Werror=format-truncation=]
  snprintf(hwaddr, 18, "00:16:3e:%02x:%02x:%02x",
                                      ^~~~
confile.c:2889:23: note: using the range [0, 4294967295] for directive argument
  snprintf(hwaddr, 18, "00:16:3e:%02x:%02x:%02x",
                       ^~~~~~~~~~~~~~~~~~~~~~~~~
confile.c:2889:23: note: using the range [0, 4294967295] for directive argument
In file included from /usr/include/stdio.h:938:0,
                 from confile.c:24:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:64:10: note: format output between 18 and 36 bytes into a destination of size 18
   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        __bos (__s), __fmt, __va_arg_pack ());
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Not sure whether the latter is really a problem. We might need an additional
fix later on.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>