In addition to being the proper POSIX etiquette, it seems like a bad idea
for issues like the one seen in #3428 to result in a kernel crash. This patch
replaces the current behavior of failing on insufficient buffer size to truncating
SOCK_RAW messages to the buffer size. This will have to change if/when MSG_PEEK
is implemented, but for now this behavior is more compliant and logical than
just bailing.