lockd: Hoist file_lock init out of nlm4svc_decode_shareargs()

lockd: Hoist file_lock init out of nlm4svc_decode_shareargs()

The xdrgen-generated XDR decoders cannot initialize the
file_lock structure because it is an internal kernel type,
not part of the wire protocol. To prepare for converting
SHARE and UNSHARE procedures to use xdrgen, the file_lock
initialization must be moved from nlm4svc_decode_shareargs()
into the procedure handlers themselves.

This change removes one more dependency on the "struct
nlm_lock::fl" field in fs/lockd/xdr4.c, allowing the XDR
decoder to focus solely on unmarshalling wire data.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>