nfsd: Initialize ssc before laundromat_work to prevent NULL dereference

In the Linux kernel, the following vulnerability has been resolved:

nfsd: Initialize ssc before laundromat_work to prevent NULL dereference

In nfs4_state_start_net(), laundromat_work may access nfsd_ssc through

nfs4_laundromat -> nfsd4_ssc_expire_umount. If nfsd_ssc isn't initialized,

this can cause NULL pointer dereference.

Normally the delayed start of laundromat_work allows sufficient time for

nfsd_ssc initialization to complete. However, when the kernel waits too

long for userspace responses (e.g. in nfs4_state_start_net ->

nfsd4_end_grace -> nfsd4_record_grace_done -> nfsd4_cld_grace_done ->

cld_pipe_upcall -> __cld_pipe_upcall -> wait_for_completion path), the

delayed work may start before nfsd_ssc initialization finishes.

Fix this by moving nfsd_ssc initialization before starting laundromat_work.