Fix several net-type bugs

[michaelortmann]

Found by: michaelortmann
Patch by: michaelortmann
Fixes: #1218

One-line summary:
fix several net-type bugs

Additional description (if needed):
net-type must be traced only in irc.mod and from there server.mod is called
in case of error, the net_type and net_type_int variables must not be changed nor Ok, set. must be logged
fatal() must only be called during bot startup

Test cases demonstrating functionality (if applicable):
before:

.set net-type 6
[09:41:11] tcl: builtin dcc call: *dcc:set -HQ 1 net-type 6
[09:41:11] #-HQ# set net-type 6
[09:41:11] * ERROR: NET-TYPE NOT SET.
 Must be one of DALNet, EFnet, freenode, Libera, IRCnet, Quakenet, Rizon, Undernet, Other.

here fatal() lets eggdrop die
after:

.set net-type 6
[12:17:14] tcl: builtin dcc call: *dcc:set -HQ 1 net-type 6
[12:17:14] #-HQ# set net-type 6
Error: can't set "net-type": Must be one of DALNet, EFnet, freenode, Libera, IRCnet, Quakenet, Rizon, Undernet, Other.

[vanosg]

@thommey comments? Is this still valid?