Update config on receiving remote SDP

[mickel8]

A couple of things still won't work e.g.:

• creating transceiver, receiving an offer, applaying this offer, creating answer etc. and then creating offer on our side. When we create our offer, we will use the transceiver configured with configuration that could be updated after receiving remote offer
• we always call update when we receive remote offer so we don't check wheter ext ids are not re-mapped
• we don't check wheter ext ids are the same across mlines

but I think this is good enough improvement to be merged

[codecov[bot]]

Codecov Report

Merging #37 (5242870) into master (604ba89) will increase coverage by 0.61%. The diff coverage is 96.90%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #37 +/- ## ========================================== + Coverage 86.72% 87.34% +0.61% ========================================== Files 14 14 Lines 633 664 +31 ========================================== + Hits 549 580 +31 Misses 84 84 ``` | [Files](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/37?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc) | Coverage Δ | | |---|---|---| | [lib/ex\_webrtc/peer\_connection.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/37?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9wZWVyX2Nvbm5lY3Rpb24uZXg=) | `84.67% <100.00%> (+0.12%)` | :arrow_up: | | [lib/ex\_webrtc/peer\_connection/demuxer.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/37?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9wZWVyX2Nvbm5lY3Rpb24vZGVtdXhlci5leA==) | `92.59% <100.00%> (ø)` | | | [lib/ex\_webrtc/rtp\_transceiver.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/37?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9ydHBfdHJhbnNjZWl2ZXIuZXg=) | `91.37% <100.00%> (-0.43%)` | :arrow_down: | | [lib/ex\_webrtc/sdp\_utils.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/37?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9zZHBfdXRpbHMuZXg=) | `88.88% <100.00%> (+0.55%)` | :arrow_up: | | [lib/ex\_webrtc/peer\_connection/configuration.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/37?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9wZWVyX2Nvbm5lY3Rpb24vY29uZmlndXJhdGlvbi5leA==) | `89.85% <94.54%> (+7.50%)` | :arrow_up: | ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/37?src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/37?src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc). Last update [604ba89...5242870](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/37?src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc).