Changes

ipa: Use pseudo-random number for SLS in IPA->M3UA direction

In Change-Id Ice7bab997b84cfed00c7d6d780c70f4e9fac6002 we introduced
code that would make the LSB of the file descriptor be used as SLS
when passing packets from IPA in M3UA direction.

This did however not achieve sufficient entropy in real-world use cases.

In this change, we change over to allocating a pseudo-random SLS to each
IPA connection at the time it is established;  We then assign that SLS
to each packet received on that IPA connection.

Change-Id: Ia4e66d660b6057338f66a47fffc8a0d32759f733
Related: SYS#6543
Closes: SYS#6802