[forwardport] fix(ios): make sure we can build an iOS release (#598) (#599)

This diff forward ports f47b0c6c16e0cd417e3591358eb85b45962f307d to master.

Original commit message:

- - -

1. we now need to name the framework `.xcframework` otherwise
gomobile refuses to build a new framework for us ¯\_(ツ)_/¯

2. remove duplicate errno definition for iOS (iOS and darwin
are considered the same, therefore we don't need iOS defs)

Reference issue for this PR: https://github.com/ooni/probe/issues/1876

This diff WILL need to be forwardported to master.

internal/netxlite/errno_linux_test.go

@@ -1,5 +1,5 @@
 // Code generated by go generate; DO NOT EDIT.
-// Generated: 2021-11-10 12:32:23.366945689 +0100 CET m=+3.126904885
+// Generated: 2021-11-15 13:49:27.048049 +0100 CET m=+0.365044251
 
 package netxlite