MFC r265157: kldxref: Clean up error reporting

MFC r265157: 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

git-svn-id: svn://svn.freebsd.org/base/stable/10@269014 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f