ims_ipsec_pcscf: more algorithms, SA improvements

[riccardv]

• add aes-cbc, des-ede3-cbc ipsec encryption algoriyhms
• improve nlmsg_seq choice for concurrent multi UEs Registrations at
  same time
• before sending replies over IPsec check the existing
  of opened TCP sockets

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)

Checklist:

• PR should be backported to stable branches
• Tested changes locally
• Related to issue #XXXX (replace XXXX with an open issue number)

Description

[miconda]

@alexyosifov - given that you contributed recently to this module, do you have any comment on this PR?

[henningw]

Thanks for the pull request, i have added one comment regarding the time handling. Are there module any documentation updates necessary as well?

[miconda]

@riccardv - I added ksr_clock_gettime() in the core/ut.h, which is portable version of clock_gettime() that works for MacOS as well. Push another commit to this PR to use it.

Any other comments from devs for this PR?

[riccardv]

Thanks @miconda , I did the correction and pushed

[alexyosifov]

@miconda , No comments from my side.