Increase size of the servername array to avoid truncated output warning.

net/sunrpc/clnt.c:582:75: error：‘%s’ directive output may be truncated
writing up to 107 bytes into a region of size 48
[-Werror=format-truncation=]
  582 |                   snprintf(servername, sizeof(servername), "%s",
      |                                                             ^~

net/sunrpc/clnt.c:582:33: note:‘snprintf’ output
between 1 and 108 bytes into a destination of size 48
  582 |                     snprintf(servername, sizeof(servername), "%s",
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  583 |                                          sun->sun_path);
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Suggested-by: NeilBrown <neilb@suse.de>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>