Roxbury native Rollins Ross recently returned from Puerto Rico where he was on tour at the San Juan Hotel and celebrating the 50th anniversary of the Martha’s Vineyard Cottagers. Despite the whirlwind travel, Ross was upbeat and relaxed when I entered his Mattapan home for our interview. His living room was filled with CDs, DVDs, a piano and music memorabilia. Although a jazz musician at heart, he loves his R&B and his long-standing band, Soul Source, will be laying rhythm an …