nfsd4: fix nfs4err_resource in 4.1 case

encode_getattr, for example, can return nfserr_resource to indicate it
ran out of buffer space.  That's not a legal error in the 4.1 case.  And
in the 4.1 case, if we ran out of buffer space, we should have exceeded
a session limit too.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>