Use strlcpy() instead of strncpy() when copying ifname to ensure

Use strlcpy() instead of strncpy() when copying ifname to ensure
that it is NUL terminated.  Additional NUL padding is not required
for short names.

Use sizeof(destination) in a few places instead of IFNAMSIZ.

Cast afp->af_ridreq and afp->af_addreq  to make the intent of
the code more obvious.

Reported by:	Coverity
CID:		1009628, 1009630, 1009631, 1009632, 1009633, 1009635, 1009638
CID:		1009639, 1009640, 1009641, 1009642, 1009643, 1009644, 1009645
CID:		1009646, 1009647, 1010049, 1010050, 1010051, 1010052, 1010053
CID:		1010054, 1011293, 1011294, 1011295, 1011296, 1011297, 1011298
CID:		1011299, 1305821, 1351720, 1351721
MFC after:	1 week