submit_sm calls should support a list of encodings

[smn]

When submit_sm_encoding is set to utf-16be hello world is encoded accordingly. This means that when we have an SMS like:

'a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a '

It's delivered as:

'\x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 \x00a\x00 '

which results in ~4 SMSs because that's 70 chars per SMS.

Somewhere there should be a flag that selects a suitable encoding based on the input because this should fit in a single SMS with utf-8.

[smn]

Not even sure what the configs for this need to look like.
Perhaps a dcs <-> encoding map like we have for deliver_sm and a separate big on the processor that tells us what dcs value we should use for a piece of string?

@hodgestar @jerith thoughts?