nfs_common: must not hold RCU while calling nfsd_file_put_local

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

nfs_common: must not hold RCU while calling nfsd_file_put_local

Move holding the RCU from nfs_to_nfsd_file_put_local to
nfs_to_nfsd_net_put. It is the call to nfs_to->nfsd_serv_put that
requires the RCU anyway (the puts for nfsd_file and netns were
combined to avoid an extra indirect reference but that
micro-optimization isn't possible now).

This fixes xfstests generic/013 and it triggering:

"Voluntary context switch within RCU read-side critical section!"

[ 143.545738] Call Trace:
[ 143.546206] <TASK>
[ 143.546625] ? show_regs+0x6d/0x80
[ 143.547267] ? __warn+0x91/0x140
[ 143.547951] ? rcu_note_context_switch+0x496/0x5d0
[ 143.548856] ? report_bug+0x193/0x1a0
[ 143.549557] ? handle_bug+0x63/0xa0
[ 143.550214] ? exc_invalid_op+0x1d/0x80
[ 143.550938] ? asm_exc_invalid_op+0x1f/0x30
[ 143.551736] ? rcu_note_context_switch+0x496/0x5d0
[ 143.552634] ? wakeup_preempt+0x62/0x70
[ 143.553358] __schedule+0xaa/0x1380
[ 143.554025] ? _raw_spin_unlock_irqrestore+0x12/0x40
[ 143.554958] ? try_to_wake_up+0x1fe/0x6b0
[ 143.555715] ? wake_up_process+0x19/0x20
[ 143.556452] schedule+0x2e/0x120
[ 143.557066] schedule_preempt_disabled+0x19/0x30
[ 143.557933] rwsem_down_read_slowpath+0x24d/0x4a0
[ 143.558818] ? xfs_efi_item_format+0x50/0xc0 [xfs]
[ 143.559894] down_read+0x4e/0xb0
[ 143.560519] xlog_cil_commit+0x1b2/0xbc0 [xfs]
[ 143.561460] ? _raw_spin_unlock+0x12/0x30
[ 143.562212] ? xfs_inode_item_precommit+0xc7/0x220 [xfs]
[ 143.563309] ? xfs_trans_run_precommits+0x69/0xd0 [xfs]
[ 143.564394] __xfs_trans_commit+0xb5/0x330 [xfs]
[ 143.565367] xfs_trans_roll+0x48/0xc0 [xfs]
[ 143.566262] xfs_defer_trans_roll+0x57/0x100 [xfs]
[ 143.567278] xfs_defer_finish_noroll+0x27a/0x490 [xfs]
[ 143.568342] xfs_defer_finish+0x1a/0x80 [xfs]
[ 143.569267] xfs_bunmapi_range+0x4d/0xb0 [xfs]
[ 143.570208] xfs_itruncate_extents_flags+0x13d/0x230 [xfs]
[ 143.571353] xfs_free_eofblocks+0x12e/0x190 [xfs]
[ 143.572359] xfs_file_release+0x12d/0x140 [xfs]
[ 143.573324] __fput+0xe8/0x2d0
[ 143.573922] __fput_sync+0x1d/0x30
[ 143.574574] nfsd_filp_close+0x33/0x60 [nfsd]
[ 143.575430] nfsd_file_free+0x96/0x150 [nfsd]
[ 143.576274] nfsd_file_put+0xf7/0x1a0 [nfsd]
[ 143.577104] nfsd_file_put_local+0x18/0x30 [nfsd]
[ 143.578070] nfs_close_local_fh+0x101/0x110 [nfs_localio]
[ 143.579079] __put_nfs_open_context+0xc9/0x180 [nfs]
[ 143.580031] nfs_file_clear_open_context+0x4a/0x60 [nfs]
[ 143.581038] nfs_file_release+0x3e/0x60 [nfs]
[ 143.581879] __fput+0xe8/0x2d0
[ 143.582464] __fput_sync+0x1d/0x30
[ 143.583108] __x64_sys_close+0x41/0x80
[ 143.583823] x64_sys_call+0x189a/0x20d0
[ 143.584552] do_syscall_64+0x64/0x170
[ 143.585240] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 143.586185] RIP: 0033:0x7f3c5153efd7