ead: replace legacy RETSIGTYPE with void in signal handler
The RETSIGTYPE macro was historically used for signal handler return types,
defaulting to int on some legacy systems. This is no longer needed,
so we now use void as the return type.
Fixes a compiler error:
error: assignment to 'void (*)(int)' from incompatible pointer type 'int (*)()' [-Wincompatible-pointer-types]
Link: https://github.com/openwrt/openwrt/pull/19681
Signed-off-by: Nick Hainke <[email protected]>
Nick Hainke