[system] Remove port number from TLS Server Name Identification (SNI). Fixes #46549...

[system] Remove port number from TLS Server Name Identification (SNI). Fixes #46549 (#4120)

The port number should not be included along the host name. Otherwise
the server will refuse the connection (and we'll throw). This is a
problem when servers are not using the default (443) SSL/TLS port.

ref: https://bugzilla.xamarin.com/show_bug.cgi?id=46549

The BTLS provider was fixed but the old MonoTLS (managed) provider had
the same issue.

Another PR will be made to fix AppleTLS in xamarin-macios repo [2]

[1] https://github.com/mono/mono/pull/3939
[2] https://bugzilla.xamarin.com/show_bug.cgi?id=45994