small fixes for ping to properly set state in case of failure (dotnet/corefx#33621)

small fixes for ping to properly set state in case of failure (dotnet/corefx#33621)

* unix ping fixes

* feedback from review and fixes for failing tests

* feedback from review

* more rework on cleanup logic

* add missing check for disposed object in Async path

* remove freebsd part of this change to make it cleaner

* await for all calls of SendPingAsyncCore()

* make arg checking synchronous and stabilize SendPingAsync_InvalidArgs failing on some platforms

* feedback from review

Commit migrated from https://github.com/dotnet/corefx/commit/2696d751a7b50bdc3e03bf5089f67aa0bd081b24