It's a brilliant double entendre. One part is calling himself a mofo. The other, "mother-suckin rock and roll" is making reference to how rock and roll became the breast to which he fed from.
Bono has a habit of taking words a phrases which have established cultural meanings and turning them on their head. It's like taking slang and idioms one step further - he used this in a bunch of songs from the 1990's.
It's a brilliant double entendre. One part is calling himself a mofo. The other, "mother-suckin rock and roll" is making reference to how rock and roll became the breast to which he fed from.