Fixes the following build warning with musl libc:
In file included from ../src/util/rfkill.cpp:24:
/usr/include/sys/poll.h:1:2: warning: #warning redirecting incorrect #include <sys/poll.h> to <poll.h> [-Wcpp]
1 | #warning redirecting incorrect #include <sys/poll.h> to <poll.h>
| ^~~~~~~