plugin: Add first as parameter to ssa_db_validate_lft in ssa_extract

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
plugin: Add first as parameter to ssa_db_compare in ssa_comparison

Due to this (and previous) change can now make first variable
in core.c static rather than global as it no longer needs to be
extern'd elsewhere.

Signed-off-by: Hal Rosenstock <hal@mellanox.com>