sctp: notify consumer if send buffer is full

[jmillan]

And new maxSctpSendBufferSize transport option

[jmillan]

NOTE:

	static size_t DefaultSctpSendBufferSize{ 262144 }; // 2^18.
	static size_t MaxSctpSendBufferSize{ 268435456 };  // 2^28.

I need to properly check those values. The first comes from the default value in my system, the second from a comment from heresctplab/usrsctp#142 (comment)

[ibc]

Here is an overview of what got changed by this pull request:

Complexity increasing per file
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- lib/DataConsumer.js  1
         

See the complete overview on Codacy