Dynamically load .so modules to expand functionality
o Dynamically load all the .so files found in /libexec/nvmecontrol and
o Link nvmecontrol -rdynamic so that its symbols are visible to the
libraries we load.
o Create concatinated linker sets that we dynamically expand.
o Add the linked-in top and logpage linker sets to the mirrors for them
and add those sets to the mirrors when we load a new .so.
o Add some macros to help hide the names of the linker sets.
o Update the man page.
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D18455