nfsd: don't alloc under spinlock in rpc_parse_scope_id

nfsd: don't alloc under spinlock in rpc_parse_scope_id

BugLink: https://bugs.launchpad.net/bugs/1951822
[ Upstream commit 9b6e27d01adcec58e046c624874f8a124e8b07ec ]

Dan Carpenter says:

  The patch d20c11d86d8f: "nfsd: Protect session creation and client
  confirm using client_lock" from Jul 30, 2014, leads to the following
  Smatch static checker warning:

        net/sunrpc/addr.c:178 rpc_parse_scope_id()
        warn: sleeping in atomic context

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: d20c11d86d8f ("nfsd: Protect session creation and client...")
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>