nfsd: Fix a perf warning

perf does not know how to deal with a __builtin_bswap32() call, and
complains. All other functions just store the xid etc in host endian
form, so let's do that in the tracepoint for nfsd_file_acquire too.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>