lockd: define nlm_port_min,max with CONFIG_SYSCTL

gcc with W=1 and ! CONFIG_SYSCTL
fs/lockd/svc.c:80:51: error: ‘nlm_port_max’ defined but not used [-Werror=unused-const-variable=]
   80 | static const int                nlm_port_min = 0, nlm_port_max = 65535;
      |                                                   ^~~~~~~~~~~~
fs/lockd/svc.c:80:33: error: ‘nlm_port_min’ defined but not used [-Werror=unused-const-variable=]
   80 | static const int                nlm_port_min = 0, nlm_port_max = 65535;
      |                                 ^~~~~~~~~~~~

The only use of these variables is when CONFIG_SYSCTL
is defined, so their definition should be likewise conditional.

Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>