
eth_addrcmp() is #defined in eth.h:
#define eth_addrcmp(a,b) (memcmp((_VOIDSTAR)&a, (_VOIDSTAR)&b, sizeof(a)))
and (obviously) returns TRUE if the two addresses are the same.
memcmp() is defined in src/lib/ansi/memcmp.c and has the prototype:
memcmp(const void *s1, const void *s2, size_t n)
memcp() compares the two n byte chunks of memory, one chunk that starts at address s1 and the other that starts at address s2.