nfs: Avoid overrun when copying client IP address string

As seen in <http://bugs.debian.org/549002>, nfs4_init_client() can
overrun the source string when copying the client IP address from
nfs_parsed_mount_data::client_address to nfs_client::cl_ipaddr.  Since
these are both treated as null-terminated strings elsewhere, the copy
should be done with strlcpy() not memcpy().

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>