Rationalize some of the variable names in Solver::Options.

lm_max_diagonal -> max_lm_diagonal
lm_min_diagonal -> min_lm_diagonal
linear_solver_max_num_iterations -> max_linear_solver_iterations
linear_solver_min_num_iterations -> min_linear_solver_iterations

This follows the pattern for the other parameters in Solver::Options
where, the max/min is the first word followed by the name of the
parameter.

Change-Id: I0893610fceb6b7983fdb458a65522ba7079596a7