SUNRPC: Fix occasional warning when destroying gss_krb5_enctypes

SUNRPC: Fix occasional warning when destroying gss_krb5_enctypes

I'm guessing that the warning fired because there's some code path
that is called on module unload where the gss_krb5_enctypes file
was never set up.

name 'gss_krb5_enctypes'
WARNING: CPU: 0 PID: 6187 at fs/proc/generic.c:712 remove_proc_entry+0x38d/0x460 fs/proc/generic.c:712

destroy_krb5_enctypes_proc_entry net/sunrpc/auth_gss/svcauth_gss.c:1543 [inline]
gss_svc_shutdown_net+0x7d/0x2b0 net/sunrpc/auth_gss/svcauth_gss.c:2120
ops_exit_list+0xb0/0x170 net/core/net_namespace.c:169
setup_net+0x9bd/0xe60 net/core/net_namespace.c:356
copy_net_ns+0x320/0x6b0 net/core/net_namespace.c:483
create_new_namespaces+0x3f6/0xb20 kernel/nsproxy.c:110
copy_namespaces+0x410/0x500 kernel/nsproxy.c:179
copy_process+0x311d/0x76b0 kernel/fork.c:2272
kernel_clone+0xeb/0x9a0 kernel/fork.c:2684
__do_sys_clone+0xba/0x100 kernel/fork.c:2825
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reported-by: syzbot+04a8437497bcfb4afa95@syzkaller.appspotmail.com
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>