connman: update musl incompatibility reason

connman no longer triggers a conflict of userspace and kernel headers since
commit 69ced963 (musl: workaround kernel if_ether.h header conflict). The
real blocker for musl build (besides a few missing includes here and there)
is the missing res_ninit() implementation. Update the comment accordingly.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>