Minor warning

[polluks]

gcc (Debian 8.3.0-6) 8.3.0

gcc -DHAVE_CONFIG_H -I. -I..  -DEUC -DSUPPORT_LH7   -g -O2 -MT header.o -MD -MP -MF .deps/header.Tpo -c -o header.o header.c
header.c: In function '_skip_bytes':
header.c:71:1: warning: type of 'len' defaults to 'int' [-Wimplicit-int]
 _skip_bytes(len)
 ^~~~~~~~~~~

https://stackoverflow.com/a/18424897/1430535