CLEANUP: tcp: stop exporting smp_fetch_src()

CLEANUP: tcp: stop exporting smp_fetch_src()

This is totally ugly, smp_fetch_src() is exported only so that stick_table.c
can (ab)use it in the {sc,src}_* sample fetch functions. It could be argued
that the sample could have been reconstructed there in place, but we don't
even need to duplicate the code. We'd rather simply retrieve the "src"
fetch's function from where it's used at init time and be done with it.