lwip: Correct comment word usage in ip4_frag.c
lwip: Correct comment word usage in ip4_frag.c

Upstream commit: a82c6122d55389e9fd758acfedffac440933e91d

johnkingsley/aprinter,johnkingsley/aprinter,ambrop72/aprinter,johnkingsley/aprinter,johnkingsley/aprinter,johnkingsley/aprinter,ambrop72/aprinter,johnkingsley/aprinter,ambrop72/aprinter,ambrop72/aprinter,johnkingsley/aprinter,ambrop72/aprinter,ambrop72/aprinter,ambrop72/aprinter