Suppose \( f \) is a function satisfying \( f(x+y)=f(x)+f(y) \) for all \( x,y \in \mathbb{N} \) and \( f(1)=\dfrac{1}{5} \). If \( \displaystyle \sum_{n=1}^{m} \dfrac{f(n)}{n(n+1)(n+2)}=\dfrac{1}{12} \), then \( m \) is equal to _________.
