Add support for Enhanced L2CAP mode to support GOEB

[akuker]

For my use case, I would like to be able to use the Generic Object Exchange Profile (GOEP). According to the GOEP specification, the L2CAP channel must be configured for Enhanced Retransmission Mode:

7.1.2 Flow and Error Control Option
The L2CAP channel for OBEX connections shall be configured to use Enhanced Retransmission Mode

The current l2cap implementation in Bumble only supports Basic flow/control mode and does not support Enhanced Retransmission Mode. Therefore will not support GOEP functions. Please update the l2cap implementation (and test cases) to support ERTM.

[akuker]

Note: I'm working on this issue and hope to have a PR soon. Feel free to assign it to me.

[barbibulle]

FYI, we will likely soon do a bit of refactoring/cleanup in the way L2CAP is handled. I hope that won't conflict too much with your work.

[akuker]

FYI, we will likely soon do a bit of refactoring/cleanup in the way L2CAP is handled. I hope that won't conflict too much with your work.

Will the interfaces to the class be changing?