Bound Telecom logging recursion

Put a bound on the recursion in Session#toString
to ensure we do not accidently cause a Stack overflow

Bug: 186694546
Test: atest TeleServiceTests
Merged-In: I52f44dd02d0d860d0894e9b84fded8cf5ff5a18e
Change-Id: I52f44dd02d0d860d0894e9b84fded8cf5ff5a18e