kldxref: Clean up error reporting

kldxref: Clean up error reporting

Omit "too many sections" warnings if the ELF file is not dynamically
linked (and is therefore skipped anyway), and otherwise output it only
once.  An errant core file would previously cause kldxref to output a
number of warnings.

Also introduce a MAXSEGS #define and replace literal 2 with it, to make
comparisons clear.

Reviewed by:	kib
Sponsored by:	The FreeBSD Foundation