tap: return an error when a PortRange's min > max

The quickcheck tests for tap that were re-enabled in PR #1042 have
caught a bug: when a `PortMatch` message has a `min` value that's
greater than its `max` value, the tests expect that `TcpMatch::try_from`
should return an error (since the range is obviously invalid). However,
we don't currently do that.

This is causing CI to break on an unrelated change:
https://github.com/linkerd/linkerd2-proxy/runs/2797285941#step:3:907

This PR adds a new test reproducing the failing quickcheck inputs, and
fixes the bug (by making `TcpMatch::try_from` return an error in that
case).

Since quickcheck inputs are randomly generated and are not
deterministic, I thought it was probably a good idea to have a
hard-coded test to reproduce this case, just in case there are future
regressions. As a side note, we may want to consider switching from the
`quickcheck` crate to the [`proptest` crate] --- one nice feature of
`proptest` is that it automatically records failing inputs, which can be
checked in to git, and future test runs will try all the failing inputs
as well as randomly generating new ones.

[`proptest` crate]: https://github.com/AltSysrq/proptest

linkerd/proxy/tap/src/grpc/match_.rs

@@ -180,7 +180,7 @@ impl TryFrom<observe_request::r#match::Tcp> for TcpMatch {
         m.r#match.ok_or(InvalidMatch::Empty).and_then(|t| match t {
             tcp::Match::Ports(range) => {
                 // If either a minimum or maximum is not specified, the range is considered to
-                // be over a discrete value.
+                // be over a discrete value.`
                 let min = if range.min == 0 { range.max } else { range.min };
                 let max = if range.max == 0 { range.min } else { range.max };
                 if min == 0 || max == 0 {
@@ -189,6 +189,9 @@ impl TryFrom<observe_request::r#match::Tcp> for TcpMatch {
                 if min > u32::from(::std::u16::MAX) || max > u32::from(::std::u16::MAX) {
                     return Err(InvalidMatch::InvalidPort);
                 }
+                if min > max {
+                    return Err(InvalidMatch::InvalidPort);
+                }
                 Ok(TcpMatch::PortRange(min as u16, max as u16))
             }