rpcapd: Fix parameter name validation in the configuration file.

Apparently, one of the changes in commit ac0abe3 lost the negation of
the test condition and made any parameter name that starts with a letter
(which is every parameter name currently implemented in rpcapd) invalid:

$ cat rpcapd.conf
NullAuthPermit = NO
$ ./rpcapd -f rpcapd.conf
rpcapd: error: rpcapd.conf, line 1 doesn't have a valid parameter name
Press CTRL + C to stop the server...

Negate the condition to fix this.

Author: infrastation

CHANGES

@@ -69,6 +69,7 @@ DayOfTheWeek, Month DD, YYYY / The Tcpdump Group
         another incorporate-remote-capture project. (issue #1120)
       rpcapd: Refine SSL options in printusage().
       Fix a possible buffer overflow (Coverity CID 1619148).
+      Fix parameter name validation in the configuration file.
     Documentation:
       Document a standard format for writing out BPF filter programs.
       Add a README.hurd.md file.

rpcapd/fileconf.c

@@ -142,7 +142,7 @@ void fileconf_read(void)
 			// Is the next character alphabetic?  If not,
 			// this isn't a valid parameter name.
 			//
-			if (FILECONF_ISALPHA(*ptr))
+			if (! FILECONF_ISALPHA(*ptr))
 			{
 				rpcapd_log(LOGPRIO_ERROR,
 				    "%s, line %u doesn't have a valid parameter name",