Enabling rbash with restricted mode

[sabi789]

Use bash with enable-restricted mode

[sabi789]

The enable_restricted feature is currently enabled in the build configuration.

• Configuration: In the configure script, opt_restricted is set to yes by default.
• Header: config.h contains #define RESTRICTED_SHELL 1, which means the support for restricted shells is compiled into the binary.
• Binary: The restricted_shell symbol is present in the bash binary.
• Runtime: While the feature is compiled in, the shell is not currently running in restricted mode (as verified by shopt restricted_shell returning off).
  This is expected unless the shell is invoked as rbash or with the -r flag. Hence soft linked bash to rbash enabling restricted mode

[sabi789]

Raised PR please check this PR #103