chanserv/set_mlock: improve logging for oper mlock

[ilbelkyr]

This addresses #832 by specifically logging changes to the oper-only subset of MLOCK (both to CMDLOG_ADMIN and wallops()).

Example log output:

<@nicole> ~set mlock +P
<@ChanServ> nicole SET:MLOCK: #services to +ntP
<@ChanServ> nicole SET:MLOCK:OPER: #services added +P

<@nicole> ~set mlock -P
<@ChanServ> nicole SET:MLOCK: #services to +nt-P
<@ChanServ> nicole SET:MLOCK:OPER: #services removed +P, added -P

<@nicole> ~set mlock +L
<@ChanServ> nicole SET:MLOCK: #services to +ntL
<@ChanServ> nicole SET:MLOCK:OPER: #services removed -P, added +L

<@nicole> ~set mlock +P-L
<@ChanServ> nicole SET:MLOCK: #services to +ntP-L
<@ChanServ> nicole SET:MLOCK:OPER: #services removed +L, added +P-L

<@nicole> ~set mlock -P
<@ChanServ> nicole SET:MLOCK: #services to +nt-P
<@ChanServ> nicole SET:MLOCK:OPER: #services removed +P-L, added -P

<@nicole> ~set mlock
<@ChanServ> nicole SET:MLOCK: #services to +nt
<@ChanServ> nicole SET:MLOCK:OPER: #services removed -P