LPC4088 Compilation Warnings

[sarahmarshy]

Inspired by: https://os.mbed.com/forum/bugs-suggestions/topic/28059/

mbed-os-example-blinky compiles with 8 warnings for this target. Half of them from LWIP, half from NXP HAL.

@0xc0170, who's the right person from NXP to tag?

[kegilbert]

I can fix up the LWIP warnings.

[kegilbert]

@sarahmarshy PR is up for LWIP and the ethernet_api fixes.

[ciarmcom]

ARM Internal Ref: MBOTRIAGE-152

[0xc0170]

5320 merged, should be resolved