MFC r270027:

tmconfig compilation when MK_ATM == yes and MK_BSNMP == no

 Makefile.inc1:
 Always compile gensnmptree with bootstrap-tools when MK_BSNMP != no
 instead of depending on a potentially stale tool installed on the build host

 sbin/atm/atmconfig/Makefile:
 - Always remove oid.h to avoid cluttering up the build/src tree.
 - Consolidate all of the RESCUE/MK_BSNMP != no logic under one
 conditional to improve readability
 - Remove unnecessary ${.OBJDIR} prefixing for oid.h and use ${.TARGET} instead
   of spelling out oid.h
 - Add a missing DPADD for ${LIBCRYPTO} when compiled MK_BSNMP == yes and
   MK_OPENSSL == yes and not compiling for /rescue/rescue

 sbin/atm/atmconfig/main.c:
 Change #ifndef RESCUE to #ifdef WITH_BSNMP in main.c to make it
 clear that we're compiling bsnmp support into atmconfig