Do more deeper LMR searches.

At expected cut nodes allow at least one ply deeper LMR search for the first seventh moves.

STC:
LLR: 2.93 (-2.94,2.94) <-0.50,2.50>
Total: 42880 W: 10964 L: 10738 D: 21178
Ptnml(0-2): 105, 4565, 11883, 4773, 114
https://tests.stockfishchess.org/tests/view/6179abd7a9b1d8fbcc4ee6f4

LTC:
LLR: 2.93 (-2.94,2.94) <0.50,3.50>
Total: 66872 W: 16930 L: 16603 D: 33339
Ptnml(0-2): 36, 6509, 20024, 6826, 41
https://tests.stockfishchess.org/tests/view/617a30fb2fbca9ca65972b5e

closes https://github.com/official-stockfish/Stockfish/pull/3770

Bench: 6295536