man: Mention eap-md5 in radtest synopsis

Add "eap-md5" to the possible values of -t option in radtest's manpage
SYNOPSIS to match the detailed description in the OPTIONS.
man: Add -P option to radtest synopsis

Add "-P" option to radtest's manpage SYNOPSIS to make it match the
OPTIONS section.
Merge pull request #822 from spbnick/radtest_man_fixes

Radtest man fixes