unix: improve solaris event port panic message
unix: improve solaris event port panic message

For golang/go#54254

Change-Id: Id59bacfabc5c818478f6a9af8d585f56f74c2bde
Reviewed-on: https://go-review.googlesource.com/c/sys/+/422099
Reviewed-by: Nahum Shalman <ea4b4769541b7a1ab9ddc5a581537404baaae831@gmail.com>
Reviewed-by: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@google.com>

golang/sys,golang/sys,golang/sys