Propagate phy::RawSocket send error to caller

[witchof0x20]

For #587

[Dirbaio]

Thanks for the PR!

Now that I look at it again (sorry!) in receive, WouldBlock errors are propagated and everything else panics (instead of returning Illegal):

smoltcp/src/phy/raw_socket.rs

Lines 75 to 76 in 61639d5

	Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => None,
	Err(err) => panic!("{}", err),

send and receive should probably be consistent, either both panic or both returning an error. I don't know in which cases can a RawSocket send/recv fail, I think they should be fairly rare since it's a "virtual" network thingy instead of actually talking to a peer, so maybe panicking is better?

[witchof0x20]

Updated with consistent behavior. I generally lean towards propagating any error, but in the name of consistency, it makes sense to have the same behavior on both. If I run into other errors, I can file a separate issue!

[Dirbaio]

Thank you!

bors r+

[bors]

Build succeeded:

• clippy
• fmt
• fuzz
• tests