MFC r325420: lld: accept EINVAL to indicate posix_fallocate is unsupported

As of r325320 posix_fallocate on a ZFS filesystem returns EINVAL to
indicate that the operation is not supported. (I think this is a strange
choice of errno on the part of POSIX.)

PR: 223383, 223440
Reported by: Mark Millard
Sponsored by: The FreeBSD Foundation