LWIP: Provide inline replacements for htons() and htonl()

[ndrs-pst]

Summary of changes

Since LWIP version 2.1.0 provide the way to supply assembly or inline replacements for htons() and htonl()

Impact of changes

CMSIS intrinsic function __REV16 and __REV will be used instead of default implementation in lwip_def.c
#define lwip_htons(x) __REV16(x)
#define lwip_htonl(x) __REV(x)

Significant reduce of code sizes and also MCU cycles 🚀

Migration actions required

None

Documentation

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Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[X] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

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[ciarmcom]

@ndrs-pst, thank you for your changes.
@ARMmbed/mbed-os-connectivity @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

I set this to patch release, if that is OK. This should not change the functionality.

[0xc0170]

CI started

[mbed-ci]

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