traceroute.8: improve the documentation of -P
- -P didn't say what the argument is supposed to be; in the case of udplite(4), "-Pudp-lite" is not valid, one must use "-Pudplite".
- be more explicit about what sort of packets we generate, particularly for -Psctp and -Pgre.
Reviewed by: imp, tuexen, des
Approved by: des (mentor)
Pull Request: https://github.com/freebsd/freebsd-src/pull/1657