Replace session pointer with refcount #191

Job	Run time
Check c99 compilation	24s
Check codebase format with clang-format	5s
Modular build on ubuntu-latest (1, 1, 1, 1)	40s
Build and test raweth transport on ubuntu-latest (1)	34s
Modular build on ubuntu-latest (1, 1, 1, 0)	35s
Build and test raweth transport on ubuntu-latest (0)	13s
Modular build on ubuntu-latest (1, 1, 0, 1)	37s
Run unit tests on ubuntu-latest	33s
Modular build on ubuntu-latest (1, 1, 0, 0)	30s
Modular build on ubuntu-latest (1, 0, 1, 1)	34s
Build and test in single thread on ubuntu-latest	27s
Modular build on ubuntu-latest (1, 0, 1, 0)	33s
Modular build on ubuntu-latest (1, 0, 0, 1)	41s
Modular build on ubuntu-latest (1, 0, 0, 0)	29s
Modular build on ubuntu-latest (0, 1, 1, 1)	26s
Modular build on ubuntu-latest (0, 1, 1, 0)	21s
Modular build on ubuntu-latest (0, 1, 0, 1)	21s
Modular build on ubuntu-latest (0, 1, 0, 0)	19s
Modular build on ubuntu-latest (0, 0, 1, 1)	21s
Modular build on ubuntu-latest (0, 0, 1, 0)	19s
Modular build on ubuntu-latest (0, 0, 0, 1)	37s
Modular build on ubuntu-latest (0, 0, 0, 0)	21s
Test multicast and unicast fragmentation	26s
	10m 26s

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