nfc: llcp: protect nfc_llcp_sock_unlink() calls

nfc_llcp_sock_link() is called in all paths (bind/connect) as a last
action, still protected with lock_sock().  When cleaning up in
llcp_sock_release(), call nfc_llcp_sock_unlink() in a mirrored way:
earlier and still under the lock_sock().

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>