nfc: Do not send datagram if socket state isn't LLCP_BOUND

As we know we cannot send the datagram (state can be set to LLCP_CLOSED
by nfc_llcp_socket_release()), there is no need to proceed further.

Thus, bail out early from llcp_sock_sendmsg().

Signed-off-by: Siddh Raman Pant <code@siddh.me>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Suman Ghosh <sumang@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>