Add an option to change BLE_ATT_ATTR_MAX_LEN

[kutu]

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For my HID device I need bigger than 512 bytes report map, currently I have to change this line https://github.com/h2zero/esp-nimble-cpp/blob/cd115f1738fbf9134a4b00ed41d36fb20cafe22c/src/NimBLEAttValue.h#L30

and in nimble as well https://github.com/apache/mynewt-nimble/blob/baf2930d32c21222b77086181d842301bff9721f/nimble/host/include/host/ble_att.h#L227

Without changing this lines I get "driver error" in Windows, because my report map is not being sent.

If there is a way to send bigger than 512 bytes report map, please advice.

Thank you.

[h2zero]

That would go against the BLE core specification.