Revert "Re-try read if it returns EAGAIN or EINTR"

This reverts commit 817eddee9fbb9a6f5a8ecbd1b3f388de10c39d6b.
Revert "Fix for TN3270 dissector, this avoids going past the DATA.len as well as using going past the 512 characters for username and password"

This reverts commit 58d293ae0068099c9af8cbee9548392a773a7564.