Fixes#9744
Appears to be a lwIP porting bug. Comments in our porting layer say:
This function should support recursive calls from the same task or interrupt. In other words, sys_arch_protect() could be called while already protected.
Save some ROM space by putting MBED_NORETURN attributes on error
functions and failed asserts.
mbed_error was documented as returning an error code. It never
actually could return, so documentation updated, but return type
kept.