Address GCC 8.3 -O3 compilation warning

Address GCC 8.3 -O3 compilation warning

Compiling with -O3 triggers the following warning with GCC 8.3:

    driver.c: In function ‘dlz_findzonedb’:
    driver.c:193:29: warning: ‘%u’ directive output may be truncated writing between 1 and 5 bytes into a region of size between 0 and 99 [-Wformat-truncation=]
      snprintf(buffer, size, "%s#%u", addr_buf, port);
                                 ^~
    driver.c:193:25: note: directive argument in the range [0, 65535]
      snprintf(buffer, size, "%s#%u", addr_buf, port);
                             ^~~~~~~
    driver.c:193:2: note: ‘snprintf’ output between 3 and 106 bytes into a destination of size 100
      snprintf(buffer, size, "%s#%u", addr_buf, port);
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Increase the size of the relevant array to prevent this warning from
being triggered.

(cherry picked from commit 44e6bb8b9318b5992194356a4898983ae10bf67c)